Monodisperse spherical rare earth oxides

Abstract

The present invention relates to a composition comprising monodisperse spherical rare-earth oxide particles having an average particle size of about 20 nm to about 300 nm. The rare-earth oxide particles in this composition have a diameter D of a calculated particle size in nanometers, which can be determined by the following formula. JPEG2026509615000020.jpg16166 Here, SSA is m 2 BET specific surface area in units of / g, ρ is g / cm² 3 The density is per unit area, and the difference from the diameter of the observed particle size measured by SEM is less than approximately 25%. The rare earth particles may be Dy2O3, Ho2O3, La2O3, and Y2O3 particles. This composition has properties beneficial for ceramic and electronic applications. Furthermore, the present invention includes a manufacturing process for these particles and applications for these particles.

Description

[Technical Field]

[0001] This application was filed as a PCT international application on 25 March 2024 (March 23, 2023, which falls on a Saturday) and claims priority and benefits of U.S. Provisional Patent Application No. 63 / 491,805, filed on 23 March 2023, the entire contents of which are incorporated herein by reference.

[0002] This specification relates to compositions of monodisperse spherical rare-earth oxide particles having an average particle size of about 20 nm to about 300 nm, processes for manufacturing these compositions, and their applications in multilayer ceramic capacitors. The rare-earth oxides in these compositions may be dysprosium oxide, holmium oxide, yttrium oxide, lanthanum oxide, or mixtures thereof. [Background technology]

[0003] Dysprosium oxide (Dy2O3), holmium oxide (Ho2O3), lanthanum oxide (La2O3), and yttrium oxide (Y2O3) have applications in the glass and optics industries. These oxides have specific applications in ceramics, glass, phosphors, lasers, and multilayer ceramic capacitors. In particular, these oxides are used as photoluminescent and thermoluminescent materials, as contrast agents in magnetic resonance imaging, and as additives to improve capacitance in the barium titanate (BaTiO3) dielectric component of multilayer ceramic capacitors.

[0004] These applications require rare-earth oxides with small particle sizes that can be obtained without grinding. Increasing efforts have been made to prepare nanooxide materials that meet the size, shape, crystal structure, and surface chemistry requirements of such technological applications.

[0005] The problem is to achieve an acceptable yield while precisely controlling the morphology (size, shape, surface chemistry, particle size distribution, etc.) when synthesizing these oxides. Therefore, increasing efforts have been directed towards the preparation of these oxides where the size, shape, crystal structure and surface chemistry meet the requirements of the technical applications of the end use.

[0006] Therefore, there is still a need to develop a simple and efficient method for preparing compositions of these rare earth oxides that have a specific morphology and particle size and are obtained in high yield.

Summary of the Invention

[0007] In the present application, a composition comprising monodisperse spherical rare earth oxide particles is disclosed. The composition has an average particle size of from about 20 nm to about 300 nm, and the rare earth oxide particles have a diameter (D) of the calculated particle size in nm determined by the following formula.

Number

[0008] In the present application, a process for the production of monodisperse spherical rare earth particles is also disclosed. The process comprises (a) mixing a rare earth salt, a polymer additive and a precipitating agent in a solvent to provide a rare earth precursor mixture, (b) subjecting the rare earth precursor mixture to a hydrothermal reaction to form a precipitate, and (c) calcining the precipitate to provide monodisperse spherical rare earth particles. The process provides monodisperse spherical rare earth oxide particles having an average particle size of from about 20 nm to about 300 nm, and the rare earth oxide particles have a calculated particle size diameter D in nm determined by the following formula.

number

[0009] [Figure 1] A flowchart of one embodiment of the process for producing monodisperse spherical rare earth oxides disclosed in this application is shown.

[0010] [Figure 2A] This is an SEM image of the Dy2O3 particles from Example 1.

[0011] [Figure 2B] This graph shows the particle size distribution (PSD) profile of the Dy2O3 particles in Example 1. It shows the single-peaked particle size distribution profile.

[0012] [Figure 2C] This is an X-ray powder diffraction (XRPD) image of Dy2O3 from Example 1 after calcination, showing the characteristics of the cubic phase.

[0013] [Figure 3A] This graph shows the PSD profile of Dy2O3 in Example 2. It shows the particle size distribution profile with a single peak.

[0014] [Figure 3B] This graph shows the PSD profile of Dy2O3 in Example 2. It shows the particle size distribution profile with a single peak.

[0015] [Figure 3C] This is the XRPD of Dy2O3 from Example 2 after calcination, showing the characteristics of a cubic phase.

[0016] [Figure 4A] This is an SEM image of Ho2O3 from Example 3.

[0017] [Figure 4B] This graph shows the PSD profile of Ho2O3 in Example 3. It shows the particle size distribution profile with a single peak.

[0018] [Figure 4C] This is the XRPD of Ho2O3 from Example 3 after calcination, showing the characteristics of the cubic phase.

[0019] [Figure 5A] This is an SEM image of Dy2O3 from Example 4.

[0020] [Figure 5B] This is the XRPD of Dy2O3 from Example 4 after calcination, showing the characteristics of a cubic phase.

[0021] [Figure 6A] This is an SEM image of Dy2O3 from Example 5.

[0022] [Figure 6B] This is the XRPD of Dy2O3 from Example 5 after calcination, showing the characteristics of the cubic phase.

[0023] [Figure 7A] This is an SEM image of Ho2O3 from Comparative Example 1.

[0024] [Figure 7B] This graph shows the PSD profile of Ho2O3 in Comparative Example 1.

[0025] [Figure 7C] This is the XRPD of Dy2O3 from Comparative Example 1 after calcination, showing the characteristics of the cubic phase.

[0026] [Figure 8A] This is an SEM image of Dy2O3 from Comparative Example 2.

[0027] [Figure 8B] This is the XRPD of Dy2O3 from Comparative Example 2 after calcination, showing the characteristics of the cubic phase.

[0028] [Figure 9A] This is an SEM image of Dy2O3 in Comparative Example 3.

[0029] [Figure 9B] This is the XRPD of Dy2O3 from Comparative Example 3 after calcination, showing the characteristics of the cubic phase. [Modes for carrying out the invention]

[0030] This application discloses a composition comprising monodisperse spherical rare-earth oxide particles having an average particle size of approximately 20 nm to approximately 300 nm. The rare-earth oxide particles have a diameter (D) in nanometer units, which can be calculated using the following formula.

number

[0031] Before compositions comprising monodisperse spherical rare-earth oxides and processes for producing such compositions are disclosed and described, it should be understood that this application is not limited to any specific structure, process step or material disclosed herein, but extends to equivalents recognized by a person of ordinary skill in the art. It should also be understood that the terms used herein are for the purpose of describing specific embodiments and are not intended to be limiting. It should be noted that in this specification, the singular forms “a,” “an,” and “the” also encompass the plural unless the context explicitly indicates otherwise. Therefore, for example, “step” may include multiple steps, “generate” or “product” should not be interpreted as meaning all products in a reaction or treatment, and “treatment” may encompass one or more such treatment steps. Thus, a “treatment” step may include multiple or repeated treatments of the same material or fluid to produce a specified treatment product.

[0032] The term "approximately" encompasses typical experimental error. As used in this application, "approximately" means within a statistically meaningful range, such as a given particle size, concentration range, time frame, molecular weight, temperature, or pH. Such a range may be within an order of magnitude, typically within 10%, and more typically within 5%. While sometimes occurring, such a range may be within the normal experimental error of the standard method used for measurement and / or determination of a given value or range. The permissible variation encompassed by the term "approximately" depends on the specific system under consideration and is readily understandable to a person of ordinary skill in the art. Where a numerical range is described herein, all integer values ​​within that range are also encompassed as embodiments of this invention.

[0033] This application relates to monodisperse spherical rare-earth oxide particles. These rare-earth oxide particles may be Dy2O3, Ho2O3, Y2O3, La2O3, or mixtures thereof. As disclosed in this application, these novel rare-earth particles exhibit a number of distinguishing physical properties and provide improved and advantageous physical properties in end applications. These end applications include multilayer ceramic capacitors.

[0034] The particles disclosed in this application are rare earth oxides. Rare earth oxides include oxides of any of the rare earth elements. Rare earth elements may be selected from cerium (Ce), yttrium (Y), lanthanum (La), neodymium (Nd), praseodymium (Pr), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), or mixtures thereof. In certain embodiments, the rare earth oxide is Dy2O3, Ho2O3, Y2O3, La2O3, or a mixture thereof.

[0035] Importantly, these particles also have an average particle size of about 20 nm to about 300 nm. In certain embodiments, these particles have an average particle size of about 20 nm to about 100 nm, or about 20 nm to about 50 nm.

[0036] Particle size analysis was performed using a Microtrac S3500 particle size analyzer. A typical measurement is performed using approximately 0.1 grams of powder sample, to which 10 ml of 2% sodium hexametaphosphate solution is added. The sample and solution are added and then sonicated for approximately 3 minutes. A few drops of the treated solution are added to the sample container of the instrument. The sample is sonicated again in the instrument for another 3 minutes. Three consecutive measurements are performed according to the instrument manufacturer's instructions. The results of the three measurements are averaged and recorded.

[0037] Laser diffraction (LD) is used to measure particle size distribution (PSD). Dynamic light scattering (DLS) is another technique that can be used to measure PSD. Both LD and DLS can be used to measure PSD, but they use different models. In DLS, the particle's velocity is a function of the particle's size. In LD, the diffraction / scattering intensity versus angle (diffraction pattern) is a function of the particle's size. Although they are based on different models, the theory of dispersion should be the same because they are merely mathematical calculations based on PSD.

[0038] The rare earth oxide particles disclosed in this application are monodisperse spherical particles. Dispersion is a measure of the heterogeneity (or homogeneity) of particle size in a mixture. This can be indicated by a polydispersity index (PDI) parameter derived from DLS or LD techniques. Specifically, the mean and standard deviation (stddev standard deviation) are obtained from the particle size distribution (PSD) profile, and (standard deviation / mean) 2It is expressed in the form of , and the PDI value is calculated. Information regarding this analysis technique can also be found at https: / / www.materials-alks.com / blog / 2017 / 10 / 23 / polydispersity-what-does-it-mean-for-dls-and-chromatography / , and is incorporated herein by reference as necessary.

Table 1

[0039] As shown in Table A, the PDI value of a completely uniform sample is 0.0. The compositions disclosed in this application are "monodisperse", which means that the PDI value of the rare earth particles is in the range of about 0.0 to 0.1.

[0040] The monodisperse spherical rare earth oxide particles of the present invention have a diameter (D) of the calculated particle size in nm, which is obtained by the following formula.

Equation

[0041] Therefore, as disclosed in this application, "monodisperse spherical" means that the rare earth oxide particles have a diameter (D) of the calculated particle size in nm, which is obtained by the following formula.

Equation

[0042] To derive this formula, the surface area of ​​the sphere is πD 2 And its volume is πD 3 This results in / 6. Therefore, the specific surface area of ​​a highly dispersed nanospherical material with a narrow particle size distribution is πD 2 ÷(πD 3 The result is ( / 6 × ρ).

[0043] In some embodiments of monodisperse spherical rare-earth oxide particles, the calculated particle size diameter (D diameter) may differ from the observed particle size diameter measured by SEM by less than approximately 20%. In certain embodiments of monodisperse spherical rare-earth oxide particles, the calculated particle size diameter (D diameter) may differ from the observed particle size diameter measured by SEM by less than approximately 15%.

[0044] In certain embodiments, the rare earth oxide particles are Dy2O3, and ρ is 7.8 g / cm³. 3 In other embodiments, the rare earth oxide particles are Ho2O3, and ρ is 8.4 g / cm³. 3 In other embodiments, the rare earth oxide particles are Y2O3, and ρ is 5.0 g / cm³. 3 In another embodiment, the rare earth oxide particles are La2O3, and ρ is 6.5 g / cm³. 3 That is the case.

[0045] As described above, the rare earth oxide particles have an average particle size of about 20 nm to about 300 nm. In some embodiments, the rare earth oxide particles may have a single-peak particle size distribution profile. In some of these embodiments, the particles have a D of about 50 nm to about 500 nm. 50 They may have. In some embodiments, the particles have a diameter of about 300 nm to about 1 μm. 99 They may have a D of about 20 nm to about 100 nm. In some embodiments, the particles have a D of about 20 nm to about 100 nm. 10 It may have.

[0046] In certain embodiments, the rare earth oxide particles are D, ranging in size from approximately 50 nm to approximately 250 nm. 50 They may have. In certain embodiments, the rare earth oxide particles are D, ranging from about 300 nm to about 850 nm. 99 They may have. In certain embodiments, the rare earth oxide particles are D, ranging from about 20 nm to about 100 nm. 10 It has.

[0047] In specifying these embodiments, the rare earth oxide particles are D, which ranges from about 120 nm to about 160 nm. 50 They may have. In these embodiments, the rare earth oxide particles are D from about 375 nm to about 750 nm. 99 They may have. In these embodiments, the rare earth oxide particles are D, ranging from about 40 nm to about 90 nm. 10 It may have.

[0048] In the embodiment, the enumerated D 10 , D 50 and D 90 Any of these ranges may be combined with each other.

[0049] In some embodiments, the rare earth oxide particles disclosed in this application have a BET specific surface area of ​​approximately 1 m². 2 From / g to approximately 70m 2 The value is / g. The apparent surface area of ​​the composition was determined using a Micromeritics Tristar II system and nitrogen at approximately 77 Kelvin. Following generally accepted procedures, in determining the surface area used herein, the application of the BET equation was limited to the pressure range in which the equation term na(1-P / P0) increases continuously with P / P0. The sample was degassed under nitrogen at approximately 350°C for approximately 2 hours.

[0050] In some embodiments, the rare earth oxide particles disclosed herein have a loss on ignition (LOI) of less than about 5% at the firing temperature. In certain embodiments, the LOI is less than about 2.5%. As described herein, the LOI was determined by measuring the sample mass before and after firing the product at 1000°C for 1 hour.

[0051] Importantly, the rare earth oxide particles disclosed in this application are spherical and do not undergo any significant aggregation. In certain embodiments, the X-ray diffraction pattern of the rare earth oxide particles may exhibit a single cubic phase with a crystalline structure, serving as an identifying fingerprint of the periodic atomic arrangement in the material.

[0052] While not bound by theory, the rare earth oxide particles disclosed in this application, particularly those having the spherical shape and size described herein, are considered to offer many beneficial technical effects, especially when used in multilayer ceramic capacitors. The unique combination of shape and size allows for better mixing and avoids significant aggregation. This improves efficiency in end applications such as multilayer ceramic capacitors. The shape and size described herein may improve the electrical performance and reliability of dielectrics. Electrical properties and associated reliability may be due to the solubility and distribution of the rare earth oxide. The shape and size described herein, as disclosed herein, may improve the solubility and distribution of rare earth oxide particles.

[0053] The rare earth oxide particles disclosed in this application are manufactured by a specific process having a diameter (D) of a calculated particle size in nanometers, which can be determined by the following formula.

number

[0054] The process disclosed in this application does not require a grinding or milling step, although grinding may be used in the disclosed process. However, even if grinding is used, it does not alter or impart the disclosed monodisperse spherical morphology. Therefore, monodisperse spherical rare earth oxide particles can be obtained without any grinding. The described process provides rare earth oxide particles having the aforementioned properties and features.

[0055] A rare earth salt, a polymer additive, and a precipitant are mixed in a solvent to provide a rare earth precursor mixture. The rare earth salt is water-soluble and is dissolved in water during this process. The salt may be a salt of a water-soluble inorganic or organic acid, such as a chloride, sulfate, nitrate, or acetate. In certain embodiments, the rare earth salt may be a chloride or nitrate. As disclosed in this application, the rare earth element of the salt may be Dy, Ho, Y, or La.

[0056] The polymer additive may be polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethyleneimine (PEI), polyethylene glycol (PEG), or a mixture thereof. The polymer additive may be any polymer that assists the processability of the rare earth precursor mixture and is removed during washing and calcination. In this specification, the role of the polymer additive is to influence particle size and morphology by providing selective surface stabilization and / or access to kinetically controlled growth conditions. The polymer additive may be added in amounts from about 5 g / L to about 100 g / L.

[0057] The precipitating agent used may be urea, biuret, aqueous ammonia, ammonium bicarbonate, ammonium oxalate, or a mixture thereof. The precipitating agent may be mixed in an amount of about 1 mole to about 100 moles per mole of rare earth.

[0058] In embodiments, the solvent may be deionized water (DI water), ethanol, methanol, acetone, or a mixture thereof.

[0059] In certain embodiments, the rare earth precursor mixture may have a rare earth concentration of about 0.05 mol / L to about 0.8 mol / L, or a rare earth concentration of about 10 g / L to about 160 g / L.

[0060] In certain embodiments, prior to step (b), the rare earth precursor mixture of step (a) may be homogenized by stirring or ultrasonic irradiation before the solution is subjected to the hydrothermal reaction in step (b). In other embodiments, homogenization may be omitted. After homogenization, the rare earth precursor mixture may be filtered and poured into a hydrothermal reactor to carry out step (b).

[0061] The rare earth precursor mixture is subjected to a hydrothermal reaction to form a precipitate. The hydrothermal reaction may be carried out at a temperature of about 80°C to about 220°C for about 1 to 12 hours. A precipitate is obtained by the hydrothermal reaction.

[0062] In certain embodiments, the precipitate may be recovered by centrifugation. In certain embodiments, the precipitate may be washed with DI water to remove bound or adsorbed residual ions such as nitrates and chlorides, and then dehydrated with a suitable solvent such as ethanol before calcination. In certain embodiments, the crystalline precipitate is free of particularly anionic impurities, characterized by having an electrical conductivity of less than about 10 μS / cm after washing.

[0063] In certain embodiments, the washed and optionally dehydrated precipitate may be dried at about 40°C to about 80°C for about 4 to about 24 hours prior to the calcination in step (c).

[0064] The precipitate is calcined to provide monodisperse spherical rare-earth oxide particles disclosed in this application. The calcination may be carried out at a temperature of about 500°C to about 1000°C for about 30 minutes to about 4 hours. The calcination should be sufficient to remove polymer additives. In certain embodiments, the calcination may be carried out at a temperature of about 575°C to about 700°C for about 45 minutes to about 1 hour 30 minutes.

[0065] The process disclosed in this application provides monodisperse spherical rare-earth oxide particles having any or all of the above-described properties and features.

[0066] The following examples illustrate in more detail the method of the present invention for the preparation and characterization of monodisperse nanospherical rare-earth oxide particles, but the scope of the present invention is not limited in any way thereto. [Examples]

[0067] In the following examples, high-resolution SEM images were acquired using a Hitachi SU5000FE-SEM, and the average particle size and morphology were determined by measuring 100 particles. Microtrac S3500 was used to determine the particle size and morphology. 10 , D 50 , D 99The degree of dispersion was determined. The crystal structure of the final product was determined using a Malvern Panalytical Empyrean X-ray diffractometer. The specific surface area (SSA) of the final product was determined using Micromeritics Tristar II. Finally, the Line of Interest (LOI) was determined by firing the sample in a muffle furnace at approximately 1000°C for approximately 1 hour.

[0068] Figure 1 is a flowchart of one embodiment of the process for producing monodisperse spherical rare-earth oxide particles, as illustrated in the following examples. Comparative Example 1: Ho2O3 without PVP

[0069] The following operations were performed. 1) 5g of urea was weighed out and dissolved in a mixture of 75ml of ethanol and 100ml of DI water. 2) The Ho precursor was prepared by dissolving 10 g of Ho(NO3)3·xH2O (TREO approximately 42%) in 175 ml of DI water. 3) The two solutions described above were mixed and sonicated at 80 kHz for 30 minutes. 4) The solution was filtered and poured into the hydrothermal reactor. 5) The mixture was treated by hydrothermal reaction at 190°C for 2 hours. 6) The precipitate was recovered by centrifugation and washed with deionized water until the conductivity was less than 10 μS / cm. 7) The solid was washed three times with ethanol and dehydrated to obtain a wet cake. 8) The wet cake was dried overnight at 60°C. 9) The dried product was calcined at 700°C for 1 hour.

[0070] The Ho2O3 particles were not monodisperse spherical as described and defined here, but rather distorted spherical. The Ho2O3 particles were observed by scanning electron microscopy (SEM) and contained distorted spherical holmium oxide particles with an average particle size of approximately 950 nm (i.e., approximately 944.9 nm by SEM) (Figure 7A). Particle size distribution analysis of these Ho2O3 particles showed that the particles were D 50 It had a particle size distribution profile with a broad single peak, with a size of 5.15 μm (Figure 7B). The calcined product was analyzed by XRPD and it was shown that the material had a cubic phase (Figure 7C). Further analyzed particles had a BET SSA of 8.99 μm. 2 The value was / g, and the BET size was 85nm. [Table 2] Comparative Example 2: Dy2O3 (WO2005026045A2) mechanically mixed with tartaric acid

[0071] The following operations were performed as disclosed in WO2005 / 026045. 1) 4.6478 g of Dy(NO3)3·xH2O was weighed out. 2) The above crystals were mixed with 5.1080 g of tartaric acid in a mortar and pestle by hand for 30 minutes. 3) The mixture was heated on a hot plate at 250°C. 4) The product was calcined at 800°C for 2 hours.

[0072] Dy2O3 particles were observed using scanning electron microscopy (SEM) (Figure 8A) and XRPD (Figure 8B). Comparative Example 3: Dy2O3 by urea precipitation (JP2005247673A)

[0073] The following operations were performed as disclosed in JP2005 / 247673. 1) 80 ml of Dy(NO3)3 solution ([Dy 3+ (Approximately 0.311M) was diluted to 200 ml with DI water. 2) 30.03 g of urea was weighed out and dissolved in DI water to make a total volume of 300 ml. 3) The two solutions described above were mixed by stirring. 4) 2.7803 g of N-oxidetrimethylamine dihydrate was added to the above solution under stirring. 5) The mixed solution was heated to 90°C and held there for 30 minutes. 6) The product was recovered by centrifugation and dried at 80°C for 2 hours. 7) The dried product was calcined at 700°C for 1 hour.

[0074] Dy2O3 particles were observed using scanning electron microscopy (SEM) (Figure 9A) and XRPD (Figure 9B). Example 1: Dy2O3 particles

[0075] The following operations were performed. 1) Measure out 5g of urea and dissolve it in 175ml of DI water. 2) The Dy precursor was prepared by dissolving 20 g of PVP (weight-average molecular weight approximately 1,300,000, manufactured by Sigma) and 10 g of Dy(NO3)3·xH2O (TREO approximately 40%) in 175 ml of DI water. 3) The two solutions described above were mixed and sonicated at 80 kHz for 30 minutes. 4) The solution was filtered and poured into the hydrothermal reactor. 5) The mixture was treated by hydrothermal reaction at 180°C for 1.5 hours. 6) The precipitate was recovered by centrifugation and washed with deionized water until the conductivity was less than 10 μS / cm. 7) The solid was washed three times with ethanol and dehydrated to obtain a wet cake. 8) The wet cake was dried overnight at 60°C. 9) The dried product was calcined at 580°C for 1 hour.

[0076] The Dy2O3 particles had a monodisperse spherical shape as defined herein. The Dy2O3 particles were observed by scanning electron microscopy (SEM) and contained spherical dysprosium oxide particles with an average particle size of approximately 100 nm (i.e., approximately 105.4 nm by SEM) (Figure 2A). Particle size distribution analysis of these Dy2O3 particles showed that the particles were D 99 As 474nm, D 50 It was shown to have a particle size distribution profile with a single peak at 131 nm (Figure 2B). The calcined product was analyzed by XRPD and it was shown that the material has a single cubic phase (Figure 2C). Further analyzed particles had a BET SSA of 8.29 nm. 2 The density was / g, and the BET size was 87nm. The monodisperse PSD profile showed that the particles were nano-sized, and D 99 474nm, D 50 This showed that it is 131 nm. [Table 3] Example 2: Dy2O3 particles

[0077] Steps 1 through 6 of Example 1 were followed, and the dried product was calcined at 700°C for 1 hour.

[0078] The Dy2O3 particles had a monodisperse spherical shape as defined herein. The Dy2O3 particles were observed by scanning electron microscopy (SEM) and contained monodisperse spherical dysprosium oxide particles with an average particle size of approximately 100 nm (i.e., approximately 103.5 nm by SEM) (Figure 3A). Particle size distribution analysis of these Dy2O3 particles showed that the particles were D 99 As 684nm, D 50 It was shown to have a peak of 145 nm and exhibit a single-peak particle size distribution profile (Figure 3B). The calcined product was analyzed by XRPD and it was shown that the material has a single cubic phase (Figure 3C). Further analyzed particles had a BET SSA of 8.18 nm.2 The density was / g, and the BET size was 88nm. The monodisperse PSD profile showed that the particles were nano-sized, and D 99 684nm, D 50 This indicated that the wavelength was 145 nm. [Table 4] Example 3: Ho2O3 particles

[0079] The following operations were performed. 1) 5g of urea was weighed out and dissolved in a mixture of 75ml of ethanol and 100ml of DI water. 2) The Ho precursor was prepared by dissolving 22 g of PVP (weight-average molecular weight approximately 1,300,000, manufactured by Sigma) and 10 g of Ho(NO3)3·xH2O (TREO approximately 42%) in 175 ml of DI water. 3) The two solutions described above were mixed and sonicated at 80 kHz for 30 minutes. 4) The solution was filtered and poured into the hydrothermal reactor. 5) The mixture was treated by hydrothermal reaction at 190°C for 2 hours. 6) The precipitate was recovered by centrifugation and washed with deionized water until the conductivity was less than 10 μS / cm. 7) The solid was washed three times with ethanol and dehydrated to obtain a wet cake. 8) The wet cake was dried overnight at 60°C. 9) The dried product was calcined at 700°C for 1 hour.

[0080] The Ho2O3 particles had the monodisperse spherical shape defined herein. The Ho2O3 particles were observed by scanning electron microscopy (SEM) and contained monodisperse spherical holmium oxide particles with an average particle size of approximately 150 nm (i.e., approximately 158.3 nm by SEM) (Figure 4A). Particle size distribution analysis of these Ho2O3 particles showed that the particles were D 99 As 409nm, D 50It was shown to have a particle size distribution profile with a single peak at 124 nm (Figure 4B). The calcined product was analyzed by XRPD and it was shown that the material has a single cubic phase (Figure 4C). Further analyzed particles had a BET SSA of 4.98 nm. 2 The density was / g, and the BET size was 143nm. The monodisperse PSD profile showed that the particles were nano-sized, and D 99 409nm, D 50 This showed that it is 124 nm. [Table 5] Example 4: Dy2O3 particles

[0081] The following operations were performed. 1) Weigh out 5.4g of urea and 11.3g of PVP, and add 37.5ml of ethanol and 69ml of Dy(NO3)3([Dy 3+ It was dissolved in a mixture of approximately 0.22 M. 2) 27.5 ml of 1 mol / L NH3·H2O and 16 ml of DI water were added to the above solution. 3) The solution was filtered and poured into the hydrothermal reactor. 4) The mixture was treated by hydrothermal reaction at 180°C for 2 hours. 5) The precipitate was recovered by centrifugation and washed with deionized water until the conductivity was less than 10 μS / cm. 6) The solid was washed three times with ethanol and dehydrated to obtain a wet cake. 7) The wet cake was dried at 60°C overnight. 8) The dried product was calcined at 700°C for 1 hour.

[0082] The Dy2O3 particles exhibited the monodisperse spherical structure defined herein. The Dy2O3 particles were observed by scanning electron microscopy (SEM) and contained monodisperse spherical dysprosium oxide particles with an average particle size of approximately 30 nm (i.e., approximately 28.3 nm by SEM) (Figure 5A). The calcined product was analyzed by XRPD, demonstrating that the material possessed a single cubic phase (Figure 5B). Further analysis of the particles revealed a BET SSA of 30.56 nm. 2 The value was / g, and the BET size was 24nm. [Table 6] Example 5: Dy2O3 particles

[0083] The following operations were performed. 1) Weigh out 6g of urea and 12g of PVP, and add 30ml of acetone and 60ml of Dy(NO3)3([Dy 3+ It was dissolved in a mixture of approximately 0.22 M. 2) 1 ml of 1 mol / L NH3·H2O and 59 ml of DI water were added to the above solution. 3) The solution was filtered and poured into the hydrothermal reactor. 4) The mixture was treated by hydrothermal reaction at 140°C for 4 hours. 5) The precipitate was recovered by centrifugation and washed with deionized water until the conductivity was less than 10 μS / cm. 6) The solid was washed three times with ethanol and dehydrated to obtain a wet cake. 7) The wet cake was dried at 60°C overnight. 8) The dried product was calcined at 700°C for 1 hour.

[0084] The Dy2O3 particles exhibited the monodisperse spherical structure defined herein. The Dy2O3 particles were observed by scanning electron microscopy (SEM) and contained monodisperse spherical dysprosium oxide particles with an average particle size of approximately 40 nm (i.e., approximately 36.0 nm by SEM) (Figure 6A). The calcined product was analyzed by XRPD, which showed that the material possessed a single cubic phase (Figure 6B). Further analysis of the particles revealed a BET SSA of 18.90 nm. 2 The value was / g, and the BET size was 38nm. [Table 7] Summary of the comparison between calculated particle size diameter and observed particle size diameter in the examples and comparative examples.

[0085] The following table summarizes the comparison between the diameter of the calculated particle size and the diameter of the observed particle size measured by SEM. As disclosed, the rare earth oxide particles disclosed in this application have a calculated particle size diameter in nanometers.

number

[0086] The results confirmed that the comparative example, manufactured using conventional methods, was significantly larger. [Table 8]

[0087] As shown, the rare earth oxide particles disclosed in this application have a calculated particle size in nanometers, diameter D:

number

[0088] The rare earth oxide particles disclosed in this application, having a particularly defined spherical shape and particle size, offer many beneficial technical effects and are particularly advantageous for use in multilayer ceramic capacitors. The combination of shape and particle size improves miscibility and prevents significant aggregation. This leads to improved efficiency in end applications such as multilayer ceramic capacitors.

[0089] Since devices such as multilayer ceramic capacitors are desired to be smaller and lighter, their components must contribute to achieving this end result. Specifically defined shapes and particle sizes can improve the electrical performance and reliability of the dielectric. Electrical properties and associated reliability may be due to the solubility and distribution of rare earth oxides. Specifically defined shapes and particle sizes can improve the solubility and distribution of rare earth oxide particles, as described herein.

[0090] The spherical morphology and particularly specified particle size defined herein may be beneficial for use as a powder, dispersion in liquid media, better mixing with BaTiO3 ceramics, and site occupancy. The particles disclosed in this application may improve electrical performance and provide high reliability. The electrical properties and associated reliability of these capacitors may be due to the solubility, distribution, and site occupancy of the rare earth oxide in BaTiO3. The rare earth oxide particles disclosed in this application, having particularly specified spherical morphology and particle size, may improve these properties.

[0091] Unless otherwise specified, all numerical values ​​used in the specifications and claims, such as the amount of components, properties like molecular weight, and reaction conditions, are understood to always be modified by the word "about." Therefore, unless otherwise specified, the numerical parameters described in the following specifications and attached claims are approximations and may vary depending on the desired properties to be obtained.

[0092] Although the numerical ranges and parameters representing the broad scope of this technology are approximations, the numerical values ​​described in specific examples are reported as accurately as possible. However, any numerical value inherently contains a certain degree of error, which is necessarily due to the standard deviation found in each test measurement.

[0093] It is clear that the compositions and methods described herein are suitable for achieving the described objectives and advantages, and the benefits inherent therein. Those skilled in the art will understand that the methods and systems described herein can be implemented in a variety of ways and are therefore not limited by the exemplary embodiments and examples described herein. In this regard, any number of features of the different embodiments described herein can be combined into a single embodiment, and alternative embodiments having fewer or more features than all of the features described herein are also possible.

[0094] While various embodiments are described for the purposes of this application, various changes and modifications can be made within the scope envisioned by this application. Furthermore, there are many other modifications that are readily conceivable to those skilled in the art, and these are also included within the scope of this application.

Claims

1. A composition comprising monodisperse spherical rare-earth oxide particles having an average particle size of approximately 20 nm to approximately 300 nm, The aforementioned rare earth oxide particles have a diameter D of a calculated particle size in nanometers, which can be determined by the following formula: Here SSA is m ２ This is the BET specific surface area in units of g, where ρ is g / cm². ３ It is the density of a unit, The diameter D of the calculated particle size is less than approximately 25% of the diameter of the observed particle size measured by a scanning electron microscope (SEM). composition.

2. The aforementioned particles are D, which ranges from approximately 50 nm to approximately 500 nm. ５０ and D from approximately 300 nm to approximately 1 μm ９９ The composition according to claim 1, having a single-peak particle size distribution profile with

3. The rare earth oxide particles are Dy ２ O ３ , Ho ２ O ３ , Y ２ O ３ , La ２ O ３ or a mixture thereof, the composition according to claim 1 or 2.

4. The aforementioned rare earth oxide particles are Dy ２ O ３ Therefore, ρ is 7.8 g / cm³. ３ The composition according to claim 3.

5. The aforementioned rare earth oxide particles are Ho ２ O ３ Therefore, ρ is 8.4 g / cm³. ３ The composition according to claim 3.

6. The aforementioned rare earth oxide particles are Y ２ O ３ Therefore, ρ is 5.0 g / cm³. ３ The composition according to claim 3.

7. The rare earth oxide particles are La ２ O ３ Therefore, ρ is 6.5 g / cm³. ３ The composition according to claim 3.

8. The composition according to any one of claims 1 to 7, wherein the difference between the calculated particle size diameter (D diameter) and the observed particle size diameter measured by SEM is less than approximately 20%.

9. The aforementioned particles are D, which ranges from approximately 50 nm to approximately 250 nm. ５０ and D from approximately 300 nm to approximately 850 nm ９９ A composition according to any one of claims 1 to 8, having the following:

10. The aforementioned particles are D, which ranges from approximately 20 nm to approximately 100 nm. １０ The composition according to claim 9, having the following characteristics.

11. The aforementioned particles are approximately 1 to approximately 70 m ２ The composition according to any one of claims 1 to 10, having a BET specific surface area of ​​1 / g.

12. The composition according to any one of claims 1 to 11, wherein the particles have a single-phase cubic crystal structure.

13. The composition according to any one of claims 1 to 12, wherein the composition has a loss on ignition (LOI) of less than about 5%.

14. A process for producing monodisperse spherical rare earth oxide particles, (a) A step of mixing a rare earth salt, a polymerizable additive and a precipitant in a solvent to obtain a rare earth precursor mixture, (b) A step of forming a precipitate by hydrothermal reaction of the rare earth precursor mixture, (c) A step of calcining the precipitate to obtain monodisperse spherical rare earth oxide particles, A process that includes this.

15. The monodisperse spherical rare-earth oxide particles have an average particle size of about 20 nm to about 300 nm. The aforementioned rare earth oxide particles have a diameter D of a calculated particle size in nanometers, which can be determined by the following formula: Here SSA is m ２ This is the BET specific surface area in units of g, where ρ is g / cm². ３ It is the density of a unit, The diameter D of the calculated particle size is less than approximately 20% different from the diameter of the observed particle size measured by SEM. The process according to claim 14.

16. The process according to claim 14 or 15, wherein the precipitating agent is selected from the group consisting of urea, biuret, aqueous ammonia solution, ammonium bicarbonate, ammonium oxalate, and mixtures thereof.

17. The process according to any one of claims 14 to 16, wherein the solvent is selected from the group consisting of deionized water, ethanol, methanol, acetone, and mixtures thereof.

18. The process according to any one of claims 14 to 17, wherein the polymer additive is selected from the group consisting of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethyleneimine (PEI), polyethylene glycol (PEG), and mixtures thereof.

19. The process according to any one of claims 14 to 18, wherein the rare earth salt is a water-soluble salt, such as a chloride or nitrate, and the rare earth is Dy, Ho, Y, or La.

20. The process according to any one of claims 14 to 19, wherein the rare earth precursor mixture of step (a) has a rare earth concentration of about 0.05 mol / L to about 0.8 mol / L, or a rare earth concentration of about 10 to about 160 g / L.

21. The process according to any one of claims 14 to 20, wherein about 1 to about 100 mol of precipitant is mixed per mol of rare earth in step (a).

22. The process according to any one of claims 14 to 21, wherein the polymer additive in step (a) is in an amount of about 5 to about 100 g / L.

23. The process according to any one of claims 14 to 22, wherein the firing in step (c) is carried out at a temperature of about 500°C to about 1000°C for about 30 minutes to about 4 hours.

24. The process according to claim 23, wherein the LOI from the firing is less than 5%.

25. The process according to any one of claims 14 to 24, wherein the hydration reaction in step (b) is carried out at a temperature of about 80°C to about 220°C for about 1 hour to about 12 hours.

26. The process according to any one of claims 14 to 25, further comprising washing the precipitate of step (b) with water and dewatering the washed precipitate before performing the calcination of step (c).

27. The process according to claim 14 or 26, wherein the rare earth precursor mixture of step (a) is homogenized by stirring or ultrasonic treatment before the hydrothermic reaction of step (b).

28. The process according to claim 26, further comprising drying the washed precipitate at approximately 40°C to approximately 80°C for approximately 4 to approximately 24 hours before performing the calcination in step (c).

29. Rare earth oxide particles produced by the process described in any one of claims 14 to 28.

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