Li/Te Co‐Doping for Synergistic Enhancement of Microwave Dielectric Properties in Calcium Tungstate Ceramics

ABSTRACT In this study, Li x Ca 1−x W 1−0.75x Te 0.75x O 4 ceramics were synthesised using a non‐stoichiometric co‐doping strategy (Li/Te = 1:0.75), systematically revealing the synergistic effect of Li and Te. During doping, Li was introduced from the decomposed secondary Li 2 TeO 4 phase, which acted as a liquid‐phase sintering aid. Density functional theory calculations confirmed that Te 4+ substitution for W 6+ enhanced the chemical bond strength and effectively passivated oxygen vacancies, promoting densification and improving dielectric properties. However, excessive doping led to the substantial decomposition/volatilisation of the secondary phase, where the volatilisation of Te outweighed its positive substitution effect, thereby degrading both structure and dielectric performance. Following optimisation, the Li 0.04 Ca 0.96 W 0.97 Te 0.03 O 4 ceramic sintered at 910°C exhibited optimal properties: εr = 9.86, Q× f = 89,613, τ f = −38.6 ppm/°C. The material also exhibited favorable dielectric characteristics in the terahertz range (0.2–1.2 THz, ε r : 4.97–6.36, tan δ: 0.009–0.0848), rendering it a potential candidate for dual‐band applications in low‐temperature co‐fired ceramic technology.