Temperature-Stable (1 – x )LaAlO ₃ – x Na _0.5 La _0.5 TiO ₃ Perovskite Ceramics with Ultra-Low Microwave Dielectric Loss

The phase structure, microstructure, microwave dielectric properties, and infrared reflection spectra of (1 – x )LaAlO 3 – x Na 0.5 La 0.5 TiO 3 ( x = 0.5–0.8) ceramics, prepared via a solid-state reaction method, were systematically investigated. All compositions formed single-phase perovskite structures, as confirmed by X-ray diffraction, and were well-sintered at 1480–1520 °C for 4 h. With increasing Na 0.5 La 0.5 TiO 3 content, the temperature coefficient of resonant frequency (τ f ) shifted from negative toward positive values. Notably, the composition with x = 0.55 exhibited near-zero τ f, demonstrating excellent temperature stability. Additionally, the lattice parameters, grain size, and relative permittivity (ε r ) increased, while the Q × f value decreased with higher x . The 0.45LaAlO 3 – 0.55Na 0.5 La 0.5 TiO 3 ceramic, sintered at 1510 °C for 4 h, achieved optimal microwave dielectric properties: ε r ∼ 31.9, Q × f ∼ 47,380 GHz, and τ f ∼ −4.7 ppm/°C. These results highlight its potential as an ultralow-loss, temperature-stable perovskite material for high-performance microwave applications.