Doped Ca(Ca_1/4A_2/4Ti_1/4)O₃ (A=Nb, Ta) Dielectrics for Microwave Telecommunication Applications

Abstract

Ca(Ca1/4A2/4Ti1/4)O3 (A=Nb, Ta) dielectric resonator materials have been prepared by the solid‐state ceramic route. The effects of various amounts of di‐, tri‐, tetra‐, penta‐, and hexavalent impurities on the structure, microstructure, density, and microwave dielectric properties of the complex perovskites have been investigated. The structure of the parent materials remained unchanged while slight increase in density was observed with a small amount of certain dopants. An improvement in dielectric constant, quality factor, and temperature coefficient of resonant frequency was observed with the doping of small amounts of MgO, ZnO, NiO, CuO, Co3O4, Cr2O3, SnO2, and Sb2O5. A correlation between the microwave dielectric properties of Ca(Ca1/4A2/4Ti1/4)O3 (A=Nb, Ta) ceramics and ionic radius of the dopant has been observed. The reported ceramics are potential candidates for dielectric resonator applications in wireless communication devices operating in the S and C bands.

Crystal Structure and Microwave Dielectric Properties of Alkaline‐Earth Hafnates, AHfO3 (A=Ba, Sr, Ca)

“…Alkaline-earth titanates (ATiO 3 ) and zirconates (AZrO 3 ) (A 5 Pb, Ba, Sr, and Ca) have played a crucial role in the development of near-zero t f MW dielectric ceramics. 7,[9][10][11][12][13][14][15][16][17][18][19] Nevertheless, these two families of simple perovskites exhibit dramatically different properties as indicated in Table I. For example, BaTiO 3 exhibits ferroelectricity, whereas SrTiO 3 and CaTiO 3 show incipient ferroelectricity.…”

Structure, Dielectric Properties, and Applications of CaTiO3-Modified Ca4MgNb2TiO12 Ceramics at Microwave Frequency

“…The microwave dielectric properties of these compounds and their solid solution were later investigated by Sebastian and colleagues and reported to possess ɛ r of 38–48, Q × f of 26 000–33 000 GHz, and τ f of 10–40 ppm/°C 11 . Research efforts have been made to tailor the microwave dielectric properties of these ceramics by suitable doping, glass addition, and a solid solution formation 12–16 . Among these compounds, Ca 4 MgNb 2 TiO 12 dielectric (ɛ r ∼37, Q × f ∼38 800 GHz, τ f ∼−32 ppm/°C) receives much more attention due to its high Q × f value and a substantially high dielectric constant 12 .…”

“…11 Research efforts have been made to tailor the microwave dielectric properties of these ceramics by suitable doping, glass addition, and a solid solution formation. [12][13][14][15][16] Among these compounds, Ca 4 MgNb 2 TiO 12 dielectric (e r B37, Q Â f B38 800 GHz, t f BÀ32 ppm/1C) receives much more attention due to its high Q Â f value and a substantially high dielectric constant. 12 Modification of t f value was also accomplished by the same group by varying the Ca/Mg ratio.…”

Low‐Temperature Synthesis and Growth of Bulk Ba2Ti9O20Ceramics on Conducting Substrates for Applications in Integrated Dielectric Resonator Devices

“…If the substrates are exposed to temperatures >200°C for a prolonged duration, ohmic contacts and material stoichiometry are degraded. Various methods such as chemical synthesis, 3–5 doping, 6 and glass fluxing 7 have been attempted to lower the process temperature of ceramics. But none of these methods can bring down the sintering temperature to the desired low values.…”

“…Ba 2 Ti 9 O 20 is a widely studied DR material [8][9][10] and has received considerable attention for its reasonably good microwave dielectric properties. However, in the preparation of Ba 2 Ti 9 O 20 , the stoichiometry of the reactants and synthesizing conditions must be precisely controlled, because there are various thermodynamically stable compounds such as Ba 6 [11][12][13][14][15][16][17][18] the effect of doping 19,20 and glass addition 21-23 on the process temperature, phase formation, and microwave dielectric properties. However, the lowest possible process temperature attained is about 9001C for Ba 2 Ti 9 O 20 -glass composites, which is much higher than what ICs can withstand.…”