Method for producing high-q microwave dielectric ceramic material based on barium lanthanoid tetratitanate
Patent Information
- Authority / Receiving Office
- RU · RU
- Patent Type
- Patents
- Current Assignee / Owner
- AKTSIONERNOE OBSHCHESTVO NAUCHNO-PROIZVODSTVENNOE PREDPRIYATIE RADIOSVYAZ
- Filing Date
- 2025-09-24
- Publication Date
- 2026-07-01
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Abstract
Description
[0001] The present invention relates to a technology for producing microwave dielectric ceramic materials based on the BaO-Ln2O3-TiO2 system.
[0002] The most famous representatives of this group of substances are barium lanthanide tetratitanates, crystallizing in the quasi-binary system BaTiO3- Ln2Ti3O9 (where Ln=Nd, Sm, etc.), which are interpreted as special cases of a solid solution with the general chemical formula Ba 6-3x (Sm 1-y Nd y ) 8+2x Ti 18 O 54 . Dielectric ceramics of composition Ba4(Sm 0.2 Nd 0.8 ) 8+4 / 3 Ti 18 O 54(where x=2 / 3, y=0.8) has high dielectric properties and is widely used as microwave resonators, ceramic substrates for strip and microstrip structures, filters in microwave communications, where high-quality ceramic dielectrics with a permittivity ε from 40 to 150 are required in combination with the lowest possible temperature coefficient of the resonant frequency τ f about 10 -6 hail -1 and low dielectric losses, - dielectric loss tangent (tgδ) < 10 -3 .
[0003] It is known that the dielectric properties of similar ceramics based on barium titanate BaTiO3 can be improved by adding various alloying elements [Niobium doping effect on BaTiO3structure and dielectric properties / V. Paunovic, VV Mitic, M. Djordjevic, Z. Prijic / / Ceramics International. - 2020. - Vol. 46. - No. 6. - P. 8154-8164.]. For example, a donor dopant replacing Ti ions4+ , are pentacharged cations with a relatively small ionic radius, for example, Nb 5+ The Nb additive varies from 0 to 5.0 mol.%. Ceramics based on barium titanate, alloyed with Nb, have a high permittivity from 1119 to 6648 depending on the concentration of the alloying additive, while the dielectric loss tangent varies from 26⋅10 -3 up to 8⋅10 -3 .
[0004] Ceramic material and method for regulating dielectric properties with the participation of Nb, considered in the analog [Niobium doping effect on BaTiO3structure and dielectric properties / V. Paunovic, VV Mitic, M. Djordjevic, Z. Prijic / / Ceramics International. - 2020. - Vol. 46. - No. 6. - P. 8154-8164.], is used to manufacture temperature-stable ceramic capacitors and is not applicable for the microwave range, since ceramics do not have the required values of permittivity (from 40 to 150), and also have high dielectric losses (tgδ is from 8⋅10 -3 up to 26⋅10 -3 depending on the composition).
[0005] In [Synthesis, Structural Characterization, and Electrical Properties of New Oxygen-Deficient Tetragonal Tungsten Bronzes Ba2NdTi 2+x Nb3-xO 15-x / 2 dx.doi.org / 10.1021 / ic301156c | Inorg. Chem. 2013, 52, 1729-1736] ceramics based on a Ba2NdTi solid solution were obtained 2+x Nb 3-x O15-x / 2 , containing niobium. Ceramics of this composition are characterized by dielectric constant values from 140 to 270 and a dielectric loss tangent of about 25⋅10 -3 in the temperature range from -150 to +200 °C. The disadvantage of the Ba2NdTi material 2+x Nb 3-x O 15-x / 2 are high dielectric losses, tgδ in the operating temperature range significantly exceeds 10 -3 .
[0006] According to the invention [RU 2209191 C1, IPC C 04 B 35 / 468 published 07 / 27 / 2003] the problem of obtaining ceramic materials with predetermined parameters required for high-frequency and microwave technology products is solved by using a method for obtaining solid solutions of the composition (Ba 1-x A x )Ln2Ti4O 12, characterized by the fact that Nd and / or Sm are used as the lanthanide Ln, the alloying element A is selected from the series Ca, Sr, Pb, in addition, an additional element B is introduced into the solid solution, replacing titanium, which is selected from the series Zr, Hf. A disadvantage of the invention is the insufficiently high achievable quality factor ε, which is about 2500. This is due to the incomplete use of the potential of isomorphic substitutions in the Ti position 4+ , and is associated with the use of only isovalent additives Zr((IV), Hf((IV).
[0007] The work, which presents data on the study of the properties of Ba ceramics, was accepted as a prototype of the claimed method based on similar features and the achieved result. 6-3x (Sm 1-y Nd y ) 8+2x Ti 18 O 54 (where x=2 / 3 and y=0.8), with a permittivity of ε≈85 [Effects of sintering conditions on microstructures and microwave dielectric properties of Ba 6-3x (Sm 1-y Ndy ) 8+2x Ti 18 O 54 ceramics (x=2 / 3) Yi Li, Xiang Ming Chen]. According to the prototype, the lowest dielectric losses (tgδ = 4.1⋅10 -4 ) and the corresponding highest quality factor (Q = 2440) were achieved for Ba4(Sm) ceramics 0.2 Nd 0.8 ) 8+4 / 3 Ti 18 O 54 (x=2 / 3 and y=0.8), sintered at 1340 °C for 12 hours.
[0008] Ceramic samples were obtained by the solid-phase method. Powders of BaCO3 (99.95), Nd2O3 (99.0), Sm2O3 (99.5), and TiO2 (99.8 wt%) were used as raw materials. Weighed raw materials were mixed in a ball mill with a zirconium lining and balls in ethanol for 24 h, and then, after drying, they were calcined at a temperature of 1200 °C in air for 3 h. The calcined powders with the addition of 8 wt% polyvinyl alcohol were pressed into products with a diameter of 12 mm and a height of 2 to 6 mm, and then sintered at a temperature of 1360 °C in air for 3-12 h.
[0009] The disadvantage of the prototype is the insufficiently high quality factor (about 2440) with the corresponding value of the dielectric loss tangent (4.1⋅10 -4 ).
[0010] The objective of the proposed invention is to obtain a ceramic microwave dielectric based on baryl lanthanide tetratitanate Ba4(Sm 0.2 Nd 0.8 ) 8+4 / 3 Ti 18 O 54 ., with low dielectric loss and high quality factor.
[0011] This is achieved by the fact that in the method for producing a high-quality microwave dielectric ceramic material based on barium lanthanide tetratitanate, which includes drying the raw components TiO2, Nd2O3Sm2O3, BaCO3 and Nb2O5 with a purity of at least 99.9 wt.%, mixing the components in a stoichiometric ratio, grinding and homogenizing the mixture in an ethyl alcohol medium, drying and annealing the resulting mixture at a temperature of 1150 ° C until the Ba4(Sm 0.2 Nd 0.8 ) 8+4 / 3 Ti 18O 54 , grinding the synthesized ceramic mass in an ethyl alcohol environment, molding and sintering the ceramics at a temperature of 1400°C for 8 hours, while niobium oxide Nb2O5 is added at the mixing stage in an amount of 0.5 to 1.5 mol.%.
[0012] The technical result is to increase the quality factor of the ceramic material based on baryl lanthanide tetratitanate Ba4(Sm 0.2 Nd 0.8 ) 8+4 / 3 Ti 18 O 54 compared to the prototype and a reduction in the dielectric loss tangent.
[0013] The essence of the invention is that the increase in quality factor and reduction in dielectric losses of Ba4(Sm) ceramics 0.2 Nd 0.8 ) 8+4 / 3 Ti 18 O 54 is achieved by alloying with niobium in an amount of 0.5-1.5 mol.%. The dielectric constant ɛ increases from 77.5 to 79.3.
[0014] The Fig. shows the dependence of the permittivity (1) and the dielectric loss tangent (2) of experimental samples for Ba4(Sm0.2Nd0.8)8+4 / 3Ti18-yNbyO54 ceramics on the concentration of the Nb alloying additive. The maximum limiting concentration of niobium oxide The difference in the proposed ceramic material is due to the fact that as this value increases (1.5 mol.%), the dielectric properties of the ceramic material deteriorate, and further increases in concentration do not lead to the desired result. The minimum niobium concentration is determined by the onset of an increase in dielectric constant and corresponds to 0.5 mol.%.
[0015] Mechanism of action of Nb 5+ is explained by the change in the concentration of predominant defects in the Ba4(Sm) compound 0.2 Nd 0.8 ) 8+4 / 3 Ti 18 O 54, which are oxygen vacancies [Synthesis, Structural Characterization, and Electrical Properties of New Oxygen-Deficient Tetragonal Tungsten Bronzes Ba2NdTi2+xNb 3- xO 15- x / 2 dx.doi.org / 10.1021 / ic301156c | Inorg. Chem. 2013, 52, 1729-1736]. When Nb 5+ occupies Ti positions 4+ , it acquires a positive charge , which must be compensated by negatively charged defects, such as cation vacancies and electrons. A response of the electron concentration is unlikely, since BLTs have a fairly large band gap. Thus, the addition of Nb increases the concentration of cation vacancies. It is known that in such cases, the content of oxygen vacancies in the anion sublattice decreases synbatically, for example, as a result of their interaction with oxygen in the gas phase according to the reaction
[0016] ,
[0017] which leads to a decrease in the concentration of free electrons. Consequently, the ceramic will exhibit better electrical insulating properties, and dielectric losses due to electrical conductivity will decrease.
[0018] The ceramics are produced by solid-phase synthesis using raw materials of TiO2, Nd2O3Sm2O3, BaCO3, and Nb2O5 with a purity of at least 99.9 wt%. Initially, the raw materials are prepared, which includes drying at 700°C for 1 hour, preparing the samples, and mixing.
[0019] The following stages are followed: grinding and homogenizing the mixture in an ethyl alcohol medium in a planetary mill; drying the mixture in air and in a drying oven at 120°C for 2 hours; annealing the resulting mixture at a temperature of 1150°C for 4 hours in order to synthesize a compound alloyed with niobium.
[0020] Then the obtained ceramic mass is ground in an ethyl alcohol environment; dried at 120°C for 2 hours; the ceramic mass is mixed with a 10% solution of polyvinyl alcohol and granulated by grinding through a sieve with a mesh size of 0.5 mm; finally, the samples are molded under a pressure of 175 to 250 MPa; natural drying for 24 hours and sintering of the ceramic samples at a temperature of 1400°C in an air environment for 8 hours.
[0021] The implementation of the method is shown in examples 1-4.
[0022] The compositions of the ceramic mass for the synthesis of experimental ceramic samples are presented in Table 1 (in terms of oxides).
[0023] Table 1 - Compositions of ceramic mass for the synthesis of experimental samples (in terms of oxides)
[0024] Compound Content, mass % (mol %) Example 1 Example 2 Example 3 Example 4 BaO 16,884 16,862 16,839 16,795 TiO2 39,575 39,325 39,076 38,581 Nb2O5 0 0,329 (0,5) 0,657 (1,0) 1,310 (2,0) Sm2O3 8,960 8,948 8,936 8,913 Nd2O3 34,582 34,536 34,491 34,401 Sum % 100 100 100 100
[0025] Example 1.
[0026] The prepared raw materials TiO2, Nd2O3Sm2O3, and BaCO3, taken in a stoichiometric ratio, are mixed and ground in an ethyl alcohol medium in a planetary mill. The mixture is then dried, briquetted, and synthesized into a ceramic mass in platinum crucibles at a temperature of 1150°C for 4 hours. The ceramic mass synthesized from powdered raw materials is ground in a planetary mill in an ethyl alcohol medium, dried, and then mixed with a 10% polyvinyl alcohol solution and granulated by grinding through a sieve with a mesh size of 0.5 mm. Then, the samples are pressed into cylinders with a diameter of 12 to 17 mm at a pressure of 175 MPa and a height of 10 mm for microwave measurements. After natural drying, the samples are sintered at a temperature of 1400°C in air for 8 hours.
[0027] Based on the results of dielectric property measurements carried out using the equipment of the state primary standard GET 110-2023 in accordance with GOST R 8.623-2015, the following data were obtained: the permittivity of the samples ε at a frequency of 2.62 GHz is 77.5; the values of the quality factor and the tangent of the dielectric loss angle are 2630 and 3.8 10 -4 , respectively.
[0028] Example 2.
[0029] The technological operations, including drying the raw components, mixing the components in a stoichiometric ratio, grinding and homogenizing the mixture, synthesizing the ceramic mass, grinding the ceramic mass in an ethyl alcohol medium, molding and sintering the ceramics, were carried out in exactly the same way as in Example 1, the difference was that at the stage of mixing the raw components TiO2, Nd2O3Sm2O3, BaCO3, an additive of niobium oxide Nb2O5 was introduced in an amount of 0.5 mol.%.
[0030] The following data were obtained: the permittivity of the samples at a frequency of 2.45 GHz is 78.0; the values of the quality factor and the dielectric loss tangent are 3030 and 3.3 10 -4 , respectively.
[0031] Example 3.
[0032] The process operations are the same as Examples 1 and 2, the difference is that the addition of niobium oxide Nb2O5 is 1.0 mol%.
[0033] The permittivity of the samples at a frequency of 2.41 GHz is 79.3; the value of the dielectric loss tangent is 3.0 10 -4 , and the quality factor is 3270, thus the quality factor increases by 20% compared to the unalloyed sample.
[0034] Example 4.
[0035] The process operations are the same as Examples 1 and 2, the difference is that the addition of niobium oxide Nb2O5 is 2.0 mol%.
[0036] The following data were obtained: at a frequency of 3.23 GHz, ε=77.7; the values of the quality factor and the dielectric loss tangent are 1786 and 5.6 10 -4 , respectively.
[0037] Table 2 shows the main properties of ceramics obtained by the proposed method (examples 1-4).
[0038]