Tailoring phase stability and high-permittivity of (1-x)(Sr0.6Na0.2La0.2Ti0.9Al0.05Nb0.05O3) -xNdAlO3 ceramic composites for C-band dielectric resonator applications

The phase stability and dielectric behavior of the (1- x )(Sr 0 . 6 Na 0 . 2 La 0 . 2 Ti 0 . 9 Al 0 . 05 Nb 0 . 05 O 3 )- x NdAlO 3 ceramic system (0.0 ≤  x  ≤ 0.5) were systematically studied and optimized through tailored ionic substitution and a conventional single-step solid-state synthesis route. This strategy enabled synergistic enhancement by modifying lattice distortions and phonon dynamics, improving microwave performance of dielectric resonator antennas for potential applications in the C-band frequency range. X-ray diffraction confirmed a stable tetragonal (P4/mmm) phase for 0.0 ≤ x  ≤ 0.5, with no secondary phases detected. Rietveld refinement and HRTEM validated solid solution formation , revealing lattice contraction and unit cell volume reduction with increasing x . Raman spectroscopy highlighted phonon modifications due to ionic substitutions. The microwave dielectric properties varied systematically, with ε r decreasing from 215 at x  = 0.0 to 36.2 at x  = 0.5 due to reduced ionic polarizability . The quality factor (Q × f) reached a maximum of 37,037 GHz at x  = 0.4 due to increased atomic packing and minimized phonon scattering. The thermal coefficient of resonance frequency (τ f ) was adjusted from 256 ppm/°C (at x  = 0.0) to −12 ppm/°C (at x  = 0.5), achieving enhanced thermal stability. The tetragonal phase at x  = 0.4 demonstrated outstanding microwave dielectric characteristics, featuring an εr of approximately 42, a Q × f value reaching 37,037 GHz, and a τ f of around −5 ppm/°C. These insights establish a clear structure-property relationship, paving the way for the development of high-performance microwave resonators.