Polycrystalline ceramic solid and method for manufacturing a polycrystalline ceramic solid

Abstract

a polycrystalline ceramic solid having a primary phase with the general composition (1-y)Pb a (Mg b Nb c )O 3‑e +yPb a Ti d O3, wherein 0.055≤y≤0.065; 0.95≤a≤1.02; 0.29≤b≤0.36; 0.63≤c≤0.69; 0.9≤d≤1.1; 0≤e≤0.1 and optionally one or more secondary phases, wherein for each cross section through the solid the area proportion of secondary phases based on the arbitrary cross sectional area through the solid is less than or equal to 0.5% or wherein the solid is free of secondary phases. Furthermore, an electrode having the ceramic solid and a device having the electrode are given and furthermore a method for manufacturing the solid and the electrode.

Description

[0001] This invention relates to a polycrystalline ceramic solid. Furthermore, this invention relates to an electrode having the ceramic solid. Finally, this invention relates to a method for manufacturing the ceramic solid and an electrode comprising the solid.

[0002] Many ceramic electrode materials are known from existing technologies. There is a high demand for materials suitable for use in electrodes and exhibiting improved performance in terms of electrode efficiency and power loss.

[0003] Therefore, the object of this invention is to provide a new material suitable for use in electrodes.

[0004] The objective is achieved by the material according to claim 1. Therefore, according to a first aspect, the present invention relates to a polycrystalline ceramic solid having

[0005] - The main phase has the following general formula:

[0006] (1-y)Pb a (Mg b Nb c )O 3-e + yPb a Ti d O3

[0007] Where 0.055 ≤ y ≤ 0.065;

[0008] 0.95 ≤ a ≤ 1.02;

[0009] 0.29 ≤ b ≤ 0.36;

[0010] 0.63 ≤ c ≤ 0.69;

[0011] 0.9 ≤ d ≤ 1.1;

[0012] 0 ≤ e ≤ 0.1;

[0013] - and any one or more secondary phases,

[0014] Wherein, for each cross section passing through the solid, the area ratio of the minor phase based on the area of ​​any cross section passing through the solid is less than or equal to 0.5%, or wherein the solid does not contain a minor phase.

[0015] Here, polycrystalline solids should be understood as crystalline solids having microcrystals, which are also referred to as grains below. These microcrystals are separated from each other by grain boundaries. The solid therefore comprises grains, which contain or are composed of the main phase material. The solid is particularly sintered.

[0016] The solid has a main phase with the following general formula:

[0017] (1-y)Pb a (Mg b Nb c )O 3-e + yPb a Ti d O 3。

[0018] This involves a single-phase system. Specifically, the lead magnesium niobate (Bleimagnesium niobate) component, Pb... a (Mg b Nb c )O 3-e , and lead titanate component, Pb a Ti d O3, together with other substances, forms a solid solution, i.e., a single phase, which is the main phase of the polycrystalline ceramic solid. This main phase is characterized by a perovskite structure.

[0019] The polycrystalline ceramic solid may have one or more other phases different from the primary phase, referred to below as secondary phases. A central feature of the invention is that the solid has only a small proportion of secondary phases or contains no secondary phases at all. Therefore, for any cross-section through the solid, the total area of ​​all secondary phases, based on the cross-sectional area through the solid, is less than or equal to 0.5%.

[0020] Preferably, the solid does not contain a secondary phase. In this case, the solid contains only a primary phase and does not have a secondary phase. In particular, the solid may consist of a primary phase.

[0021] In principle, a minor phase can be understood as an independent phase that differs from the major phase in composition. Without being bound by theory, a minor phase can be a Mg-rich phase with a composition different from the major phase, such as Mg... 2 / 3 Nb 1 / 3 O3- phase. Mg-rich secondary phases have a higher Mg content compared to the primary phase. For example, a Mg-rich secondary phase may also be lead-poor, i.e., it has a lower Pb content than the primary phase.

[0022] However, for example, a secondary phase can also be a Pb-rich secondary phase, that is, a secondary phase with a higher Pb content relative to the primary phase.

[0023] Because the minor phase differs from the major phase in its elemental composition, the area proportion of the minor phase based on the cross-sectional area through the solid can be quantified using an elemental distribution image. This elemental distribution image can be obtained using REM-EDX measurements (REM stands for scanning electron microscopy; EDX stands for energy-dispersive X-ray spectroscopy).

[0024] The polycrystalline ceramic solid according to the invention is characterized by high mechanical stability. Therefore, components formed from this material, such as electrodes, are robust and durable.

[0025] Furthermore, the solid according to the invention exhibits a high breakdown voltage. This is important for its safe application as an electrode material.

[0026] The solid according to the invention is particularly suitable as an electrode material due to its high dielectric constant and capacitance.

[0027] The composition of the described main phase enables unexpectedly high capacity in the temperature range of 20 to 45 °C, particularly 30 to 42 °C. This high capacity within this range is particularly advantageous for use in a range of ceramic electrodes. The maximum capacity can be variably set, for example, by the proportion of lead titanate, y, in the following formula.

[0028] (1-y)Pb a (Mg b Nb c )O 3-e + yPb a Ti d O3

[0029] By selecting y within the range of 0.055 ≤ y ≤ 0.065, a ceramic solid that achieves the maximum capacitance within the body temperature range of mammals can be obtained.

[0030] The inventors have realized that by using the γ content, the capacity can be matched to the respective operating temperature of the electrodes. Therefore, the maximum capacity can be set for each desired operating temperature.

[0031] Solids with a y content of 0.055 ≤ y ≤ 0.065 are suitable for electrodes operating in a temperature range of 20 to 45 °C. A y content of 0.055 to 0.065 is particularly advantageous, especially in the temperature range of 30 to 42 °C, for example at temperatures of 35 and 40 °C (e.g., 37 °C). Electrodes based on this composition not only exhibit very high capacity within the stated temperature range but also possess very low loss factors and minimal self-heating.

[0032] The polycrystalline ceramic solid according to the present invention differs from conventional ceramic solids in that it has no minor phase or only a very small proportion of minor phase. The inventors of the present invention have observed that a significant proportion of minor phase exists in ceramic solids containing a major phase with comparable chemical composition, manufactured in a conventional manner.

[0033] The inventors of this invention also determined in experiments that these secondary phases reduce the capacitance of the solid. However, high capacitance is precisely what is desired when used in electrodes.

[0034] Furthermore, the inventors of this invention were able to observe experimentally that, when used in high-capacity ceramic electrodes, the secondary phase present in conventional ceramic solids leads to poor power loss. This results in higher energy loss and therefore lower efficiency.

[0035] Furthermore, the high electrical losses and their output as heat result in self-heating of the solid. This self-heating is undesirable. It is a consequence of energy loss in the form of waste heat and implies low efficiency. Moreover, self-heating is also undesirable because the heat in the environment surrounding the electrodes may cause damage or be perceived as uncomfortable upon touch.

[0036] By setting the proportion of the secondary phase to less than or equal to 0.5% (based on the area ratio measured by any cross-sectional area through the solid), the inventors of this invention were able to improve the dielectric constant and capacitance. Improved power loss is also achieved, which improves efficiency when used in ceramic electrodes and reduces undesirable self-heating.

[0037] The smaller the proportion of the minor phase in the solid, the more pronounced these beneficial effects become.

[0038] Furthermore, the inventors of this invention were able to observe that the optical appearance of the ceramic solid could also be altered by avoiding a significant proportion of secondary phases. Therefore, conventional ceramic solids with similar compositions typically exhibit a pale yellow hue. In contrast, the ceramic solid according to this invention does not possess a comparable yellow hue.

[0039] The smaller the proportion of the minor phase in the solid, the smaller the proportion of the pale yellow color. That is, the pale yellow hue reflects the presence of the minor phase. In contrast, the ceramic solid according to the invention is characterized by a slightly beige hue.

[0040] According to one embodiment of the polycrystalline ceramic solid of the present invention, for each cross-section through the solid, the area ratio of the minor phase based on the area of ​​any cross-section through the solid is less than or equal to 0.3%, preferably less than or equal to 0.1%, more preferably less than or equal to 0.05%, and particularly preferably less than or equal to 0.01%. Most preferably, the polycrystalline ceramic solid does not contain a minor phase.

[0041] The smaller the proportion of the minor phase in the solid, the higher the dielectric constant and capacitance, and the lower the power loss. Therefore, a smaller proportion of the minor phase also results in less self-heating. In addition, as the proportion of the minor phase decreases, the pale yellow hue of the ceramic solid decreases.

[0042] According to one embodiment, the solid does not contain pyrochlore, for example, a stable cubic pyrochlore phase Pb3Nb4O. 13If free Nb2O5 is present during sintering or if PbO is lacking, a pyrochlore phase will particularly appear.

[0043] According to one embodiment, the solid according to the invention does not have a Mg-rich and / or Nb-rich minor phase, especially not a Mg-rich minor phase. For example, without considering a theoretically bound exact formula, the solid does not contain Mg. 2 / 3 Nb 1 / 3 O3 phase. This secondary phase is likely to be generated mainly in the absence of Pb during sintering, especially through the PbO exhaust gas (Abgasen) during sintering.

[0044] According to another embodiment, the solid according to the invention does not have a Pb-rich secondary phase. The inventors have recognized that not only Pb deficiency but also Pb excess can lead to the formation of undesirable secondary phases. Pb-rich secondary phases, like other secondary phases described previously, result in reduced capacitance.

[0045] One embodiment relates to a solid according to the invention, wherein the following applies: 0.057 ≤ y ≤ 0.063, for example, y equals 0.06.

[0046] Another embodiment relates to a solid according to the invention, wherein the following applies to the coefficient a:

[0047] 0.96 ≤ a ≤ 1.02, preferably 0.97 ≤ a ≤ 1.01, further preferably 0.97 ≤ a ≤ 1.00, and most preferably a = 1.0.

[0048] One embodiment relates to a solid according to the invention, wherein for the coefficient b: 0.31 ≤ b ≤ 0.36. Preferably, for b: 0.33 ≤ b ≤ 0.35.

[0049] One embodiment relates to a solid according to the invention, wherein for the coefficient c: 0.63 ≤ c ≤ 0.68. Preferably, for c: 0.64 ≤ c ≤ 0.66. If c is less than 0.68, especially less than 0.66, the ceramic solid according to the invention does not have an increased to slightly decreased Nb content, which is advantageous for avoiding the pyrochlore phase.

[0050] Another embodiment relates to a solid according to the invention, wherein for the coefficient d: 0.95 ≤ d ≤ 1.05, preferably d = 1.0.

[0051] One embodiment relates to a ceramic solid according to the invention, wherein for e: 0 ≤ e ≤ 0.09. Preferably, e equals 0. In this case, the following general formula applies to the composition of the main phase:

[0052] (1-y)Pb a (Mg b Nb c )O3 + yPb a Ti d O3

[0053] Depending on the valence of, for example, niobium in the first component, the following situation may occur: component (1-y)Pb a (Mg b Nb c The oxygen content of O3 differs slightly from a value of 3 up to a value less than 3. This difference is preferably less than 0.09. Typically, there is no significant difference, and e equals 0.

[0054] Another embodiment relates to a solid according to the invention, wherein the main phase has grains or is composed of grains with an average grain size d. 50 A value greater than 4.0 μm, preferably greater than 4.5 μm, and especially preferably greater than 5.0 μm, is measured by static image analysis as the median value of numerical correlation.

[0055] For example, the average particle size d 50 The micrometer value is 4.0-9 μm, preferably 4.5-8 μm, further preferably 5.0-7 μm, and especially preferably 5.0-6.0 μm, which is measured by static image analysis as the median value of numerical correlation.

[0056] Preferably, in static image analysis, individual grains are determined by average diameter based on the so-called kreisäquivalent diameter (ECD). The grains or microcrystals of the polycrystalline solid have an irregular three-dimensional structure. A 2D projection of the grains (EDX / EBSD overlay image) can be obtained using EDX / EBSD analysis in a scanning electron microscope. In this way, the grain size can be represented by the area of ​​the 2D projection of the grain. Finally, the ECD can be determined from the area mentioned above. For this purpose, the area corresponding to the diameter of the circle of the measured 2D projection of the grain is calculated. Therefore, in this application, the average grain size is determined by area averaging.

[0057] A larger average grain diameter results in larger "domains" in the solid, which are regions in which electric dipoles have the same orientation. This, in turn, leads to a larger dipole moment and thus a higher dielectric constant ε in the solid. This is a combined effect that results in an overall increase in the capacitance of the polycrystalline ceramic solid. Therefore, the larger the average grain size, the higher the capacitance.

[0058] The inventors of this invention have determined that by implementing a method to avoid secondary phases, a large average particle size d can be obtained simultaneously. 50 (Measured as the median of numerical correlation via static image analysis) polycrystalline ceramic solids. Therefore, avoiding secondary phases and preparing larger grains are correlated and can improve the electrical properties of ceramic solids.

[0059] According to one embodiment, the solid has pores. However, the solid according to the invention preferably exhibits low porosity overall and therefore tends not to significantly absorb moisture, which would undesirably affect electrical properties. For example, the pore volume, based on the total volume of the solid, can be less than 10%, preferably less than 5%, and particularly preferably less than 2%. It is also conceivable that the solid is non-porous. The small tendency to absorb moisture is reflected by the open circuit potential (OCV = open circuit potential) obtained by impedance measurement in a salt solution.

[0060] According to one embodiment, the solid has a compressive density of 4 to 5.5 g / ml, preferably 4.5 to 5.9 g / ml, for example 4.8 g / ml.

[0061] According to one embodiment, the ceramic solid according to the invention has a impedance greater than 10 within the range of impedance measurement. 8 Ohm's DC resistance.

[0062] According to one embodiment, the solid according to the invention has a breakdown voltage greater than 4000 V in a liquid environment. This makes it safe to use.

[0063] According to one embodiment, the ceramic solid has a capacitance exceeding 50 nF, particularly exceeding 52 nF, for example 52-58 nF, in a temperature range of 30-42°C at 200 kHz and 1 V. According to another embodiment, the maximum capacitance of the ceramic solid is at least 53 nF, for example 53-58 nF, in a temperature range of 30-42°C at 200 kHz and 1 V.

[0064] According to one embodiment, the solid according to the invention does not have cracks visible to the human eye. The composition according to the invention has good homogeneity and stability, thereby preventing crack formation.

[0065] A second aspect of the invention relates to an electrode having a polycrystalline ceramic solid as described in the first aspect of the invention and an electrical contact further applied to said solid.

[0066] A ceramic solid forming electrode according to the present invention having electrical contact.

[0067] According to one embodiment, the electrode according to the invention has exactly one ceramic solid according to the invention and exactly one electrical contact.

[0068] According to one embodiment, the electrical contact is made of a precious metal, particularly silver, or is composed of silver. Silver is not easily corroded even when exposed to high temperatures. Furthermore, it is solderable and easy to process.

[0069] According to one embodiment, the electrical contact is firmly connected to one side of the ceramic solid and can only be separated from the ceramic solid by a tensile force greater than 35 N. Therefore, an electrode with a particularly tensile-resistant contact is obtained.

[0070] A third aspect of the invention relates to a method for manufacturing a polycrystalline ceramic solid, the polycrystalline ceramic solid having

[0071] - The main phase has the following general formula:

[0072] (1-y)Pb a (Mg b Nb c )O 3-e + yPb a Ti d O3

[0073] Where 0.055 ≤ y ≤ 0.065;

[0074] 0.95 ≤ a ≤ 1.02;

[0075] 0.29 ≤ b ≤ 0.36;

[0076] 0.63 ≤ c ≤ 0.69;

[0077] 0.9 ≤ d ≤ 1.1;

[0078] 0 ≤ e ≤ 0.1;

[0079] - and any one or more secondary phases,

[0080] Wherein, for each cross-section through the solid, the area ratio of the minor phase, based on the area of ​​any cross-section through the solid, is less than or equal to 0.5%, or wherein the solid does not contain a minor phase.

[0081] The method includes the following steps:

[0082] A) Provide raw materials containing the following elements: Mg, Nb, Ti, and Pb;

[0083] B) Preparation of a mixture comprising the raw materials

[0084] C) Calcination of the mixture to prepare a calcined mixture.

[0085] E) Process the calcined mixture into green blanks.

[0086] F) Sintering the green body,

[0087] Among them, to control lead balance

[0088] - Step F) is performed in a closed system, and / or

[0089] - In another step prior to step A) or step F), an excess of raw material containing Pb is added.

[0090] Polycrystalline ceramic solids produced by this method are especially solids according to the first aspect of the invention. All ceramic solid embodiments described in this context as advantageous may also be considered as further embodiments in terms of method.

[0091] The term "closed system" in this invention should be understood in particular as a system that does not exchange gases with the surrounding environment, such as a container that can be roughly formed into a capsule.

[0092] The method according to the invention allows for the avoidance of unwanted secondary phases by controlling the lead balance.

[0093] Conversely, in conventional methods, uncontrolled lead loss occurs during sintering. Pb can be vented, particularly as PbO, during sintering in the furnace. Therefore, Pb is removed from the green at high sintering temperatures, which locally leads to the formation of Pb-depleted or Mg-rich secondary phases. In the method according to the invention, this is prevented either by adding excess lead prior to the sintering process or by sintering in a closed system that effectively prevents PbO venting. These two measures can also be combined, as even in a closed system, a limited amount of PbO can be transferred to the gas phase, even when saturated and unable to leave the closed system. The combination of Pb excess and simultaneous sintering in a closed system can particularly effectively reduce or completely avoid secondary phases. An initial Pb excess further helps to prevent the pyrochlore phase from becoming a secondary phase.

[0094] The inventors of this invention have determined that the method according to the invention unexpectedly not only achieves the avoidance of secondary phases but also results in a larger particle size of the polycrystalline ceramic solid. Along with the avoidance of undesirable secondary phases, this enables an increase in the dielectric constant of the obtained ceramic solid. Furthermore, improved capacitance and more favorable power loss are achieved, as well as the avoidance of an undesirable pale yellow hue.

[0095] The raw materials provided in step A) can be, for example, oxides, hydroxides, carbonates, nitrates, acetates, or comparable salts of elements Mg, Nb, Ti, and Pb. Oxides of elements Mg, Nb, Ti, and Pb are preferred, as are oxides of two or more of these elements. These compounds are generally commercially available at reasonable prices or can be prepared without significant experimental costs.

[0096] According to one embodiment of the method of the present invention, a first raw material is provided in step A), which is a raw material containing Mg and Nb. If the first raw material is Mg... 1 / 3 Nb 2 / 3 O2 is the preferred choice. Mg is also used. 1 / 3 Nb 2 / 3 Using O2 as the primary raw material helps avoid undesirable pyrochlore phases, such as Pb3Nb4O. 13 As a secondary phase. If Mg is chosen... 1 / 3 Nb 2 / 3 If O2 is used as the first raw material, the process can also be called the Columbit-Methode method.

[0097] According to one embodiment of the method of the present invention, the process for manufacturing Mg is carried out before step A). 1 / 3 Nb 2 / 3 O2 (a separate step A0). Mg 1 / 3 Nb 2 / 3 O2 can be produced, for example, from magnesium oxide (MgO) and niobium oxide (Nb2O5), for example by wet milling, followed by drying (filter press, spray drying), then calcination and optionally a final milling step.

[0098] According to one embodiment of the method of the present invention, a second raw material, which is a Ti-containing raw material, is provided in step A). ​​TiO2 is preferably used as the second raw material. TiO2 is relatively inexpensive and readily available.

[0099] In another embodiment of the method according to the invention, a third raw material, which is a Pb-containing raw material, is provided in step A). ​​Pb oxides, PbO and Pb3O4, have been particularly proven to be very suitable. They allow for good reaction execution and facilitate the control of lead balance.

[0100] According to one embodiment, the third raw material is Pb3O4. Pb3O4 decomposes at temperatures starting from about 500°C, releasing PbO in the process. Pb3O4 is less toxic than PbO, thus improving operational safety. By choosing Pb3O4 instead of PbO, reaction vessels and reactors can be constructed more safely. This is particularly important for the large-scale and industrial production of ceramic solids.

[0101] According to one embodiment, the raw materials in step A) are provided in stoichiometric proportions to each other. In this case, step F) is carried out in a closed system to prevent Pb loss due to PbO venting during sintering.

[0102] According to another embodiment, in step A), all non-Pb-containing raw materials are provided in stoichiometric proportions to each other, while an excess of Pb-containing raw materials is added. The inventors of this invention have determined that the Pb excess in step A) can avoid Pb-depleted or Mg- and / or Nb-rich secondary phases.

[0103] According to a preferred embodiment, an excess of Pb-containing raw material (or a third raw material) is selected such that the Pb content of all the provided raw materials is equal to the composition of the main component to be obtained ((1-y)Pb). a (Mg b Nb c )O 3-e + yPb a Ti d Each 1 mol of Pb contains at most 0.02 mol of O3.

[0104] The preferred excess is 0.01 mol to 0.02 mol. The inventors of this invention have observed that, in the case mentioned last, both Pb-depleted and Pb-rich secondary phases can be avoided particularly well.

[0105] According to an extended scheme, the Pb-containing feedstock is PbO. In this case, the amounts of feedstock provided are such that their stoichiometry theoretically yields the following general formula for the composition after the reaction without Pb loss:

[0106] (1-y)Pb a (Mg b Nb c )O 3-e + yPb a Ti d O 3 + xPbO,

[0107] Where a to e are defined as given above, and where 0 ≤ x ≤ 0.02 applies. Preferably, 0 < x ≤ 0.02 applies, and more preferably, 0.01 ≤ x ≤ 0.02 applies. Therefore, by adding at most 0.02 mol of PbO in excess, the composition has at most 0.02 mol of excess Pb per mol of Pb in the main phase.

[0108] Similarly, Pb3O4 can be added in excess to replace PbO. If the Pb-containing feedstock is Pb3O4, then Pb3O4 is added in an excess of up to 0.0067 mol per mol of Pb to achieve the desired composition of the major component. Since 1 mol of Pb3O4 releases 3 mol of PbO, this is equivalent to an excess of up to 0.02 mol of Pb. It is preferable to add an excess of Pb3O4 of 0.0033 mol to 0.0067 mol. This proportion of Pb3O4 in the feedstock is particularly suitable to avoid secondary phases and obtain good particle size.

[0109] According to one embodiment, in step B) of the method, the mixture is prepared by means of grinding the raw materials, particularly by wet grinding. In the case of wet grinding, the raw materials are pulverized in a suspension, such as an aqueous suspension.

[0110] Continue grinding until the raw material has a particle size of d. 50 Particle size d is defined as powder or suspension with a particle size of <1.5 μm, preferably <1 μm. 50 The median value of numerical correlation is measured through static image analysis.

[0111] Mixtures with the aforementioned particle sizes produce good results in further processing. They allow for good and thorough mixing and make it easier to achieve good homogeneity during calcination.

[0112] According to one embodiment of the method of the present invention, wet grinding is followed by a drying step (B1). This drying step is used to prepare for calcination.

[0113] According to one embodiment, the calcination step C) is carried out at a temperature of 800 to 860°C, for example, 840°C. These temperatures ensure effective removal of moisture.

[0114] According to an extension of the previously mentioned implementation, the calcination step C) is not carried out in the closed system according to step F), such as, for example, a closed container. This is not necessary because the given temperature is not high enough to cause significant PbO loss. However, in principle, the calcination step can also be carried out in a closed system.

[0115] According to one embodiment, the method according to the invention includes step D), wherein TiO2 and / or Nb2O5 are added to the calcined mixture. Step D) is preferably performed after step C) and before step F).

[0116] Adding TiO2 and / or Nb2O5 can shift or regulate the maximum capacitance of the ceramic solid depending on temperature.

[0117] Furthermore, the addition of TiO2 and / or Nb2O5 in step D) allows excess lead, for example in the form of PbO, to be consumed within the calcined mixture by forming a perovskite phase. Therefore, adding TiO2 and / or Nb2O5 in step D) is another way to control the lead balance. For example, it allows the initial excess Pb to be incorporated, which helps to avoid the pyrochlore phase, by incorporating TiO2 and / or Nb2O5 in step D), decomposing the initial excess Pb and thus preventing the risk of excess Pb in the finished solid. The latter leads to a decrease in dielectric constant or capacity.

[0118] According to one embodiment, the proportion of TiO2 and / or Nb2O5 added based on the calcined mixture is at most 0.4% by weight, preferably 0.001 to 0.4% by weight, more preferably 0.01 to 0.4% by weight, and particularly preferably 0.1 to 0.4% by weight, based on the weight of the calcined mixture.

[0119] One embodiment relates to a method according to the invention, wherein an excess of a raw material containing Pb is added in step A), and wherein the method according to the invention simultaneously includes step D) after step C), wherein TiO2 and / or Nb2O5 are added to the calcined mixture. Furthermore, it is preferred that step F) is carried out simultaneously in a closed system. Instead of evaporating excess lead, TiO2 and / or Nb2O5 can be added, for example, in step D), thereby binding the excess lead. This has the advantage of resulting in a significantly more homogeneous polycrystalline ceramic solid overall, compared to evaporating excess PbO in the sintering step. Lead diffuses in the solid at a rate several orders of magnitude slower than in the gas phase. This results in excess PbO near the surface leaving the solid much faster during sintering than PbO that can diffuse further from the interior of the solid. In particular, if sintering is not carried out in a closed system, a particularly large amount of PbO will evaporate. This difference in diffusion rate leads to localized heterogeneity in the solid, which in turn favors the formation of undesirable secondary phases. Therefore, it is particularly advantageous to compensate for excess Pb, for example, in step A), by adding TiO2 and / or Nb2O5 in step D), while sintering is carried out in a closed system.

[0120] One embodiment relates to a method according to the invention, including step E):

[0121] - Grinding the calcined mixture,

[0122] - Add a binder to the calcined mixture.

[0123] - Spray drying of a calcined mixture with a binder to prepare ceramic granules.

[0124] - Press the ceramic granules to prepare a green body.

[0125] Preferably, the calcined mixture is further ground until a d50 particle size is obtained that is <2 μm, preferably <1 μm, for example about 0.8 µm, as the median value measured by static image analysis. Optionally, in step E), the TiO2 and / or Nb2O5 added in the optional step D) are ground together with the calcined mixture. Fine grinding is beneficial for obtaining homogeneous green bodies.

[0126] Based on the weight of the calcined mixture, the proportion of the adhesive is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight, especially 2 to 4% by weight, for example 3% by weight. The adhesive may be, for example, a PVA adhesive (PVA = polyvinyl alcohol).

[0127] Ceramic granules were obtained by spray drying a calcined mixture with a binder, from which green bodies could be manufactured by pressing.

[0128] The green body is transformed into a ceramic solid according to the first aspect of the invention by sintering according to step F).

[0129] According to one embodiment of the method of the present invention, step F) is performed at a maximum temperature of 1150 to 1280°C. For example, the method can be performed at a maximum temperature of 1250°C.

[0130] According to one implementation, the highest temperature during step F) is maintained for 1 to 6 hours, for example, 4 hours.

[0131] These temperatures and holding times during sintering not only allow the raw materials to react completely, but also enable the resulting ceramic solid to have good homogeneity, which helps to avoid unwanted secondary phases.

[0132] According to one embodiment of the method of the present invention, step F) is carried out in a closed system, wherein the closed system is a closed container.

[0133] The term "closed container" in this invention should be understood in particular as a container in which no gas exchange occurs between its internal space and the surrounding environment.

[0134] According to one embodiment, the container has a height of 10-40 cm, for example 15-25 cm, a width of 20-50 cm, for example 25-35 cm, and a depth of 30-50 cm, for example 35-45 cm.

[0135] According to one embodiment, the sealed container has at least one material selected from Al2O3, ZrO2 and MgO, or the container is composed of one of these materials.

[0136] The sealed container preferably contains MgO or is composed of MgO. The inventors have found that MgO is particularly suitable because it exhibits exceptionally high sealing properties against PbO and does not tend to absorb PbO. For example, MgO achieves better sealing against PbO compared to conventional container materials (e.g., cordierite or mullite). Unlike other metal oxides, MgO is particularly unpredictable in absorbing PbO. This results in better shielding compared to conventional container materials, thus better prevention of PbO venting compared to other materials (e.g., cordierite or mullite as container materials).

[0137] According to one embodiment, the enclosed container has a container body and a container plate, which preferably contain or are composed of the material mentioned above.

[0138] According to one embodiment, multiple green blanks are sintered simultaneously in the closed container. For example, multiple stacks of green blanks can be sintered simultaneously in the closed container. For example, 5 to 25 stacks, each containing 5 to 30 green blanks, can be sintered in the container. Due to the presence of multiple green blanks, PbO saturation is achieved more quickly in the closed container in this manner, thereby avoiding excessively high undesirable lead losses.

[0139] A preferred embodiment relates to a method according to the invention, wherein the enclosed container has an internal space in which one or more green blanks are arranged, such that, based on the volume of the internal space, the volume fill of all green blanks is at least 30% by volume, preferably at least 40% by volume.

[0140] Volumetric fill factor is a ratio of the total volume of all green blanks arranged in and sintered within the internal space of a closed container, based on the total volume of the internal space of the container.

[0141]

[0142] If there is only one green blank in a closed container, then the "volume of all green blanks" is equal to the volume of that single green blank. If there are multiple green blanks in a closed container, then the "volume of all green blanks" is equal to the sum of the volumes of the green blanks arranged in the interior space of the closed container.

[0143] A volume fill percentage of 0% means that the closed container is empty, i.e., it does not contain any green pieces. A volume fill percentage of 100% means that the container is completely filled with one or more green pieces, with no gaps.

[0144] The inventors of this invention have observed that a volumetric filling degree of at least 30 vol% is particularly well-suited for maintaining low Pb loss during sintering. With a volumetric filling degree of at least 30 vol%, PbO saturation in the internal space of the closed container can be achieved rapidly. In this way, further PbO transfer to the gas phase becomes difficult. This allows the excess Pb preferably present in the green body to decompose slowly and in a controlled manner during sintering. Therefore, Pb deficiency in the resulting ceramic solid can be reduced or completely avoided, which is beneficial for avoiding undesirable secondary phases. The smaller the volumetric filling degree of the container, the more PbO in the internal space of the closed container transfers to the gas phase, and the more difficult it becomes to control the lead balance.

[0145] A volume filling of at least 40% is even better. This allows for particularly effective control of lead balance.

[0146] According to another embodiment, the volume fill percentage is less than 60% by volume. The inventors have recognized that it is advantageous for the volume fill percentage to not exceed 60% by volume. If the volume fill percentage is higher, it becomes difficult to arrange the green bodies in a closed container so that they are sufficiently separated from each other for sintering together.

[0147] According to a particularly preferred embodiment, the volumetric filling percentage is 30 to 60% by volume, preferably 40 to 60% by volume. In this case, neither a significant excess of Pb nor a large deficiency of Pb is observed in the resulting ceramic solid according to the invention, which leads to the avoidance of Pb-rich and Pb-poor secondary phases.

[0148] The inventors observed that, for example, in a container containing MgO, a green body volume filling of 45% resulted in only about 0.6% by weight loss of the green body due to the evaporation of PbO. Such a small lead loss enables excellent lead balance control and thus effectively avoids undesirable secondary phases.

[0149] According to one embodiment, the volume fill percentage is at least 30% by volume, and the first raw material is Mg. 1 / 3 Nb 2 / 3O2, and the raw material containing Pb is Pb3O4, in which Mg 1 / 3 Nb 2 / 3 The molar ratio of O2 to Pb3O4 is 1:0.34 to 1:0.38, preferably 1:0.35 to 1:0.37, more preferably 1:0.355 to 1:0.36, for example 1:0.356 to 1:0.358. These framework conditions allow for excellent lead balance control while maintaining high safety requirements, resulting in ceramic solids free of minor phases and achieving excellent values ​​in terms of capacity and power loss. Furthermore, in this case, the Ti-containing raw material can be, for example, TiO2, and Mg... 1 / 3 Nb2 / 3 The ratio of O2 to the amount of Ti-containing raw material can be, for example, 1:0.055 to 1:0.065.

[0150] According to one embodiment, sintering is carried out in a furnace equipped with a closed container. Another important effect of the method according to the invention is that the furnace used for sintering is protected from PbO exhaust gases by using a closed container in step F). Lead-containing exhaust gases cause the furnace lining to absorb a significant amount of lead over time. This leads to damage to the materials used for the lining. Since these typically contain silicates or aluminosilicates, they are prone to "vitrification" upon lead ingestion. However, other properties of the furnace lining are also impaired by Pb ingestion. Due to lead ingestion, the lining becomes brittle over time, develops cracks, and must be replaced. The inventors of the present invention have recognized that this can be prevented particularly effectively by sintering in a closed container preferably containing or composed of the aforementioned materials.

[0151] The fifth aspect of the invention relates to a method for manufacturing an electrode according to the second aspect of the invention, comprising a method for manufacturing a polycrystalline ceramic solid according to the fourth aspect of the invention, and including a subsequent step for providing electrical contact to the solid.

[0152] According to one embodiment, electrical contact is achieved by applying and calcining a paste, wherein the calcination is preferably carried out at a temperature of 680 to 760°C. The paste is preferably a silver paste. Silver is also corrosion-resistant and solderable at high temperatures, and allows for a strong bond with polycrystalline ceramic solids.

[0153] General Synthesis Examples

[0154] The methods according to the fourth and fifth aspects of the invention will be further explained below with the aid of exemplary synthetic routes.

[0155] Select the stoichiometry of the raw materials to be provided so that they conform in quantity to the following formulation:

[0156] 0.94*Pb(Mg 1 / 3 Nb 2 / 3 O3 + 0.06*PbTiO3 + x*PbO

[0157] Where 0 ≤ x ≤ 0.02.

[0158] The composition of the main phase is composed of at most 0.02 mol of PbO per 1 mol of Pb, which is eventually reduced during sintering.

[0159] Here, the manufacturing process involves using raw materials containing Mg and Nb, such as Mg... 1 / 3 Nb 2 / 3O3 is the starting material, for example, according to the so-called niobite process. Here, Mg and Nb-containing raw materials are wet-milled (particle size d50 < 1 µm) with Pb-containing raw materials such as Pb3O4 and Ti-containing raw materials such as TiO2, dried, and calcined at a temperature of 800-860 °C. For this purpose, it is preferable to provide an excess of Pb-containing raw materials. Optionally, the final conversion powder (Umsatzpulver) is finely milled together with (additional) TiO2 or Nb2O5 (0 to 0.4 wt% based on the weight of the conversion powder) and a binder such as PVA binder is incorporated. The resulting mixture is then spray-dried to produce compressible ceramic granules. The granules are pressed into green bodies and sintered. Sintering is carried out at 1150-1280 °C, where this sintering temperature is maintained for 1-6 hours. To control lead balance, sintering is carried out in a closed container, for example in the form of capsules made of MgO, with a volume filling degree > 30% by volume.

[0160] Here, the container may specifically have a container body and a container plate. The container body and the container plate are combined with each other to form the container. They are arranged to overlap each other, thereby closing the container.

[0161] This method can be easily scaled up for mass production by using appropriately large containers or a large number of containers in the sintering furnace. The method yields polycrystalline ceramic solids free of minor phases.

[0162] During the pressing process, a polycrystalline ceramic solid geometry can be formed. Electrical contacts are obtained through metallization. For this purpose, a silver paste is preferably used to obtain electrical contacts containing or composed of Ag. The paste is calcined at a temperature of 680-760°C and is brazable.

[0163] Attached Figure

[0164] The invention is further explained below with the aid of the accompanying drawings. A comparison is made here between a conventional polycrystalline ceramic solid (reference material) and a polycrystalline ceramic solid (sample) according to the invention:

[0165] Figure 1A and 1B The conventional ( Figure 1A ) and according to the present invention ( Figure 1B Scanning electron microscope (BSE) images of solids.

[0166] Figure 2A and 2B The conventional ( Figure 2A ) and according to the present invention ( Figure 2B Scanning electron microscope (SE) images of solids.

[0167] Figure 3A and 3B The conventional ( Figure 3A ) and ceramic solids according to the present invention ( Figure 3B Image of the elemental distribution of magnesium on ().

[0168] Figure 4A and 4B The main phase of conventional ceramic solids is shown ( Figure 4A ) and secondary phase ( Figure 4B A table of EDX results composed of elements of ).

[0169] Figure 5 The results (EDX results) of the elemental composition of the main phase of the ceramic solid according to the present invention are shown.

[0170] Figure 6A and 6B The conventional ( Figure 6A ) and the solid according to the invention ( Figure 6B EDX / EBSD overlay image (EBSD = electron backscatter diffraction).

[0171] Figure 7A and 7B It shows the conventional ( Figure 7A ) and the solid according to the invention ( Figure 7B The evaluation results of the granularity.

[0172] Figure 8 The capacitance relative to temperature of the polycrystalline ceramic solid according to the present invention and conventional polycrystalline ceramic solids having a minor phase are shown.

[0173] Figure 9 The relationship between the loss factor and temperature is shown for polycrystalline ceramic solids according to the present invention and conventional polycrystalline ceramic solids with minor phases.

[0174] Figure 10A and 10B A container with gaps is shown. Figure 10A ) and completely sealed containers ( Figure 10B (These can be used to manufacture samples and to manufacture solids corresponding to reference materials.)

[0175] These figures and results will be described in detail below:

[0176] Figures 1A to 2B Each image is a scanning electron microscope (SEM) image. These, along with other SEM images and measurements described below, were obtained on a Zeiss Merlin Compact VP scanning electron microscope. All four images were taken at 1000x magnification, with an accelerating voltage of 20 kV, at approximately 2.2 x 10⁻⁶ ppm.-6 Recording was performed in a vacuum of mbar. Both the sample and the reference were polycrystalline ceramic solids. Both the sample and the reference were sawn, embedded, ground, and polished for scanning electron microscopy (SEM) imaging. To avoid charging, a thin carbon layer was vapor-deposited onto the microscope sections.

[0177] Figure 1A and 1B The reference material is shown. Figure 1A ) and samples ( Figure 1B A contrasting image of backscattered electrons (BSE image; BSE = backscattered electrons). Conversely, Figure 2A and 2B The reference material is shown. Figure 2A ) and samples ( Figure 2B A contrast photograph of the secondary electron (SE photograph; SE = secondary electron). Figure 1A and 2A The BSE and SE images each record the same site of the reference. Similarly, Figure 1B and 2B BSE and SE images record the same location on the sample. BSE images allow for good material contrast (phase contrast), while SE images provide more morphological information. Dark areas are visible in the BSE images of the reference and sample. These dark areas are primarily attributable to porosity, as both the sample and reference have a certain, albeit negligible, porosity. Conversely, the light background can be attributed to the dominant phase, respectively.

[0178] As mentioned earlier, SE images can provide conclusions about the surface morphology of the solid under study. Figure 2A and 2B The dark areas that can also be seen in the BSE photos can also be seen in the SE photos, but Figure 2A The SE photograph of the reference material can distinguish two different types of dark areas, while... Figure 2B Different types of dark areas cannot be seen in the image. Figure 2A It includes dark regions with light-colored boundaries and dark regions without light-colored boundaries. Dark regions with light-colored boundaries can be attributed to holes. The light-colored boundaries are caused by changes in morphology within the hole region. However, Figure 2A It also has dark areas without light-colored boundaries, which should be attributed to a secondary phase rather than pores, as will be explained in further detail below. Figure 2A China and Figure 1A In the diagram, darker areas belonging to secondary phases are marked with circles. In contrast, in... Figure 2BOnly pores can be identified, but secondary phases cannot. The reference material is characterized by a substantial proportion of secondary phases, while the sample according to the invention has no secondary phases. Figure 1A and 2A The secondary phases marked in the middle are characterized by partially needle-like or angular structures. They have a different chemical composition from the light-colored primary phase that otherwise forms the background of the photograph. This is made particularly clear by studying the chemical composition of the primary and secondary phases of the reference and the chemical composition of the only primary phase of the sample (Figures 3-5).

[0179] Figure 3A and 3B It shows the reference material ( Figure 3A ) and samples ( Figure 3B An elemental distribution image of magnesium was obtained by means of REM-EDX measurements (EDX stands for Energy Dispersive X-ray Spectroscopy). An Oxford SDD 80 mm² detector (Aztec) was used for the EDX measurements. This image shows the distribution of magnesium in the reference and the sample prepared according to the method of the present invention. This elemental distribution image again shows the same regions already shown in Figures 1 and 2. Lighter-colored regions indicate a higher proportion of magnesium. From Figure 3A and 3B The comparison revealed that the reference material has Mg-rich sites. Therefore, the minor phase present in this reference material is a Mg-rich minor phase. The proportion of the minor phase in the polycrystalline ceramic solid of this reference material can also be quantified using elemental distribution images. Evaluation of the Mg elemental distribution images on conventional ceramic solids showed a high proportion of undesirable minor phases. Therefore, this reference material has a minor phase, which, in the case of a cross-section of the solid, represents an average area proportion of 0.7% based on the cross-sectional area through the solid. In contrast, Figure 3B The ceramic solid according to the present invention has no Mg-rich sites. It has no secondary phases.

[0180] Furthermore, additional elemental distribution images for C, O, Ti, Nb, and Pb were recorded for both the reference and the sample. Notably, the elemental distribution image (Pb Mα1 image) for lead in the Mg-rich minor phase region belonging to the reference reveals lead depletion relative to the major phase. It is clear from the various elemental distribution images that the sample does not contain the undesirable minor phase, while the reference has a Mg-rich and simultaneously Pb-depleted minor phase. Figure 4A , 4B Tables 5 and 6 summarize the most important results regarding the elemental composition of the major phases of the studied samples and references, as well as the elemental composition of the minor phases of the references.

[0181] Figure 4A and 4B The EDX results of comparative scanning electron microscopy obtained from the reference are shown, in which Figure 4A The EDX results of the main phase of the ceramic solid were reproduced. Figure 4B The EDX results of the minor phases of this ceramic solid were reproduced. Figure 5 The EDX results from comparative scanning electron microscopy of the samples are shown. Four EDX spectra were recorded for each sample. For each spectrum, the measured proportions of elements O, Mg, Ti, Nb, and Pb were plotted as atomic percentages. The average proportions of Mg, Ti, Nb, and Pb were derived from each of the four spectra. Empirically, the proportions of lighter elements (such as oxygen) are underestimated in EDX measurements. Therefore, normalization was performed in a suitable manner to determine the empirical formulas such that the total content of Mg + Ti + Nb corresponds to 1. The coefficients of the relevant chemical formulas thus obtained are also available from the tables. For the major phases, coefficients based on the initial weight expectations are also given. Figure 4A and 5 The comparison shows that, in the case of the sample according to the invention, the lead ratio deviates less from the ideal composition. The lead content of the main phase of the reference is 0.941, significantly lower than the ideal value of 1.0. In contrast, the main phase of the sample is significantly closer to the ideal value. Finally, it can be seen from... Figure 4B The chemical composition of the minor phase was determined. As mentioned above, the minor phase is rich in Mg and poor in Pb. The Nb content is slightly higher than that in the major phase. Without being bound by theory, it seems most likely that the chemical composition is determined by the formula Mg... 2 / 3 Nb 1 / 3 The O3 phase describes the secondary phase.

[0182] Figure 6A and 6B The reference material is shown. Figure 6A ) and samples ( Figure 6B EDX / EBSD stacked images (EBSD = electron backscatter diffraction) were obtained. Forward Scatter Detector (FSD) was used for recording. EBSD measurements were performed on etched samples. The following settings were selected for both the reference and sample: accelerating voltage 20.00 kV; sample tilt (degrees) 69.99°; hit rate 94.25% to 94.99%; recording speed 66.25 to 66.35 Hz. The recorded phase was based on the Pb(Mg) phase. 1 / 3 Nb 2 / 3 O3: a = 4.05 Å; b = 4.05 Å; c = 4.05 Å; α = 90.00°; β = 90.00°; γ = 90.00°; Space group 221; ICSD database. These images make it particularly easy to compare the grain size of the reference and sample crystallites. This sample is characterized by a significantly larger grain size.

[0183] exist Figure 7A and 7B The figures illustrate a quantitative assessment of particle size differences. The determination of the equal circular diameter (ECD) has already been explained above. These figures particularly demonstrate that the sample according to the invention, with a diameter of 5.32 μm... Figure 7B It has a larger diameter than the reference material with a diameter of 3.79 μm. Figure 7A ) significantly larger d 50 The median value of the numerical correlation was measured via static image analysis. Therefore, compared to the reference sample, the overall particle size distribution in the sample shifted towards larger particle sizes. This indicates that the method according to the invention for preparing the sample not only avoids secondary phases but also simultaneously produces larger crystallites, thereby achieving improved capacity. Figure 8 and lower power loss () Figure 9 ).

[0184] Figure 8 The capacitances of the sample and the reference were compared. These graphs show the dependence of capacitance, given in nanofarads [nF], on temperature, given in degrees Celsius [°C]. Measurements were performed at 200 kHz and 1 V, respectively. Both solids exhibited maximum capacitance over a temperature range of 30 to 42 °C. This is attributed to the chemical composition of the comparable major phases. The measurement curves obtained from the comparison clearly show that the capacitance of the sample is consistently significantly higher than that of the reference throughout the entire measurement temperature range. The capacitance of the sample according to the invention is on average about 5% higher.

[0185] Figure 9 The dependence of the dissipation factor on temperature, given in degrees Celsius [°C], is shown. The measurements were performed individually at 200 kHz and 1 V. For both the sample and the reference, the dissipation factor decreased with increasing temperature. However, unlike the reference, the dissipation factor was significantly lower over the important temperature range of 20 to 45 °C, implying low power loss when the solid according to the invention is used in the electrode. This results in higher efficiency and, in particular, less self-heating.

[0186] Figure 10A and 10B This demonstrates how the reference material and sample depicted in Figures 1-9 can be obtained. The sample is a polycrystalline ceramic solid according to the first aspect of the invention, obtained by means of the method according to the fourth aspect of the invention. Here, the sintering step F) is performed on a container having a container body (1) and a container plate (2) according to... Figure 10BThe process is carried out in a container. Together they form a closed container, in which the sintering step F according to the method of the invention is carried out in its internal space (3). For this purpose, one or more green blanks are arranged in the internal space (3) of the closed container. The closed container forms a closed system that prevents PbO from being discharged as waste gas. The shape of the container can be varied. The material of the container is chosen so that it is not suitable for absorbing PbO and PbO is impermeable, so that the lead balance during sintering can be controlled particularly effectively. In contrast, conventional polycrystalline ceramic solids required for high-capacity electrodes for treating patients are not sintered with adequate control of the lead balance. This results in PbO being discharged as waste gas during sintering, and thus leads to heterogeneity in the solid. In particular, the inventors of the present invention were able to discover that this is responsible for the formation of undesirable secondary phases, as can be found in conventional ceramic solids. Secondary phases lead to reduced capacity and give conventional ceramic solids a yellow hue. The consequences of the lack of lead balance control are shown by example of a reference. The reference can be obtained by sintering in accordance with the method of the invention. Figure 10A It is obtained by sintering in the arrangement. Figure 10A The diagram shows a container body (1) and a container plate (2), as well as a device for providing a gap (4) between the container body and the container plate. Therefore, Figure 10A The container has a gap. The size of this gap is 5 mm. Therefore, some gas exchange can occur between the internal space (3) of the container and the surrounding environment. This results in a portion of the Pb in the solid being released as PbO during sintering. In contrast to the sample, the reference obtained in this way has a yellow hue.

[0187] Synthesis of Samples and References

[0188] The sample and reference were obtained as follows:

[0189] In both cases, green bodies with the same composition are first manufactured. For this purpose, 34.9494 kg of Mg is weighed in each case. 1 / 3Nb 2 / 3 O2, 83.8043 kg Pb3O4, and 1.7488 kg TiO2. The raw materials were pre-milled in 100 L of deionized water to a target particle size d50 of approximately 1.0 µm. The resulting mixture was then spray-dried. The mixture was then calcined at 820 °C for 6 hours, milled to a particle size d50 of approximately 0.8 μm, and spray-granulated with 3 wt% PVA binder.

[0190] Green bodies were manufactured by pressing ceramic granules. The compressive density was 4.8 g / ml. The green bodies were decarburized at 450°C.

[0191] By according to Figure 10B Samples were obtained by sintering in a closed MgO container. This was achieved by... Figure 10AThe reference material was obtained by sintering in an MgO container. The gap here was 5 mm. The sintering temperature was 1250 °C for each sample. The holding time at 1250 °C was 4 hours. In the case of the sample, the volume fill factor was approximately 45% by volume.

[0192] This invention is not limited to the description provided by way of embodiments. Rather, the invention includes each new feature and each combination of features, particularly each combination of features in the present patent claims, even if the feature or combination itself is not expressly given in the present patent claims or embodiments.

Claims

1. A method for manufacturing a polycrystalline ceramic solid, said polycrystalline ceramic solid having - The main phase has the following general formula: (1 - y)Pb a (Mg b Nb c )O 3-e + yPb a Ti d O3 in 0.055 ≤ y ≤ 0.065 0.95 ≤ a ≤ 1.02; 0.29 ≤ b ≤ 0.36; 0.64 ≤ c ≤ 0.69; 0.9 ≤ d ≤ 1.1; 0 ≤ e ≤ 0.1; - and any one or more secondary phases, Wherein, for each cross-section passing through the solid, the area proportion of the minor phase, based on the area of ​​any cross-section passing through the solid, is less than or equal to 0.5%. Or, the solid described herein does not contain a secondary phase. The method includes the following steps: A) Provide raw materials containing the following elements: Mg, Nb, Ti and Pb; B) Prepare a mixture comprising the raw materials; C) Calcination of the mixture to prepare a calcined mixture; D) Add TiO2 and / or Nb2O5 to the calcined mixture; E) Process the calcined mixture into green blanks; F) Sintering the green body, Among them, to control lead content - Step F is performed in a closed system.

2. The method according to claim 1, wherein in step A) or in another step prior to step F), an excess of a raw material having Pb is added.

3. The method according to claim 1 or 2, wherein in step A) a first feedstock is provided, which first feedstock is Mg 1 / 3 Nb 2 / 3 O2.

4. The method according to claim 1 or 2, wherein a second raw material is provided in step A), the second raw material being TiO2.

5. The method according to claim 1 or 2, wherein a third raw material is provided in step A), the third raw material being PbO or Pb3O4.

6. The method according to claim 1 or 2, wherein the mixing of the raw materials in step B) is carried out by means of wet milling.

7. The method according to claim 1 or 2, wherein the calcination in step C) is carried out at a temperature of 800 to 860°C.

8. The method according to claim 1 or 2, wherein the proportion of TiO2 and / or Nb2O5 added in step D) based on the weight of the calcined mixture is 0.01 to 0.4 by weight.

9. The method according to claim 1 or 2, wherein step E) comprises: - Grinding the calcined mixture, - Add a binder to the calcined mixture. - Spray drying of a calcined mixture with a binder to prepare ceramic granules. - Press the ceramic granules to prepare a green body.

10. The method according to claim 1 or 2, wherein step F) is performed at a temperature of 1150 to 1280°C.

11. The method according to claim 1 or 2, wherein the closed system is a closed container (1, 2).

12. The method of claim 11, wherein the sealed container comprises or is composed of at least one material selected from or formed thereof: Al2O3, ZrO2 and MgO.

13. The method of claim 11, wherein the closed container (1, 2) has an internal space (3) in which one or more green blanks are arranged, such that the volume fill of all green blanks in the internal space (3) of the closed container, based on the volume of the internal space (3), is at least 30% by volume.

14. The method according to claim 13, wherein the volume fill of all green blanks in the internal space (3) of the closed container is at least 40% by volume, based on the volume of the internal space (3).

Images