Microwave dielectric properties and crystal structure of homologous compounds ALa4Ti4O15 (A = Ba, Sr and Ca) for base station applications

Homologous compounds ALa4Ti4O15 (A = Ba, Sr and Ca) with high dielectric constant ϵr and quality factor Q × f are candidate materials for dielectric resonators in base station of telecommunication systems. We have investigated the relationship between the microwave dielectric properties and crystal structure of these new materials. Single crystals of CaLa4Ti4O15 were synthesized to analyze the crystal structure precisely. The ceramic discs of the ALa4Ti4O15 (A = Ba, Sr and Ca) were also synthesized and the microwave dielectric properties were measured. Ba-analogy showed the highest ϵr of 44.4 due to the large cationic movement. Ca-analogy showed the highest Q × f of 50,246 GHz due to resemblance in ionic radius between Ca2+ (r = 1.34 Å: 12-coordination) and La3+ (r = 1.36 Å: 12-coordination) ions. Sr-analogy showed near zero temperature coefficient of resonant frequency τf of −8.4 ppm/°C compared with the others. The relationships between their crystal structures and properties were discussed.