Crystal structure, phase compositions and microwave dielectric properties of Gd1-xCaxV1-xMoxO4 ceramics

Gd 1- x Ca x V 1- x Mo x O 4 (0 ≤ x  ≤ 1) solid-solution/composite ceramics with low permittivity were synthesized via the solid-state reaction method, and their crystal structures, phase compositions, and microwave dielectric properties were investigated. As the substitution of Ca 2+ and Mo 6+ increased, phase evolutions were observed: tetragonal zircon ( I 4 1 / amd ) for x  < 0.2, a mixture of tetragonal zircon and scheelite (0.2 ≤ x  ≤ 0.8), and tetragonal scheelite ( I 4 1 / a ) for x  > 0.8. GdVO 4 , a tetragonal zircon, exhibited a low ε r (11.48) and a near-zero τ f (−13.2 ppm/°C), yet its Q  ×  f value is suboptimal (9400 GHz). This limitation stems from its low structural stability, attributed to the prevalent edge-sharing polyhedra and high magnetic susceptibility of Gd. With the increased substitution of Ca 2+ and Mo 6+ , the Q  ×  f value of Gd 1- x Ca x V 1- x Mo x O 4 ceramics rose to 79,300 GHz ( x  = 1), while the τ f value concurrently dropped to −61.7 ppm/°C. The inherent factors affecting the microwave dielectric properties were determined by Raman scattering and infrared reflection (IR) spectra, dielectric temperature spectrum, magnetic susceptibility, and thermal expansion analysis.