Microwave dielectric properties of Ca4La2Ti5O17–LaAlO3 system ceramic materials

Compositions in the (1 − x) Ca₄La₂Ti₅O₁₇–xLaAlO₃ system were prepared in order to modify the positive temperature coefficient of the resonant frequency (τ _f ) of Ca₄La₂Ti₅O₁₇. The microwave dielectric properties and phase composition of this system ceramics were investigated. X-ray powder diffraction results showed that Ca₄La₂Ti₅O₁₇ and LaAlO₃ formed a solid solution only when x ≤ 0.2. The τ _f values showed a near linear decrease with increasing additions of LaAlO₃. It was observed that near zero τ _f value can be achieved as x = 0.64. The permittivity (ε_r) and the quality factor (Q × f) values exhibited a non-linear behavior with LaAlO₃ additions. The microwave dielectric properties were strongly correlated with composition, secondary phases and grain sizes. For practical application, a permittivity (ε_r) of 42, a quality factor (Q × f value) of 12,450 GHz and a temperature coefficient of resonant frequency (τ _f ) of ~0 ppm/°C for 0.36 Ca₄La₂Ti₅O₁₇−0.64 LaAlO₃ were proposed.