Phase evolution, crystal structure, and microwave dielectric properties of gillespite‐type ceramics

A gillespite‐structured M CuSi 4 O 10 ( M  = Ba 1‐ x Sr x , Sr 1‐ x Ca x ) ceramics with tetrahedral structure (P4/ncc) were prepared by solid‐state reaction method. X‐ray diffraction and thermogravimetry with differential scanning calorimetry (TG‐DSC) were employed to study the phase synthesis process of BaCuSi 4 O 10 . Pure BaCuSi 4 O 10 phase was obtained at 1075°C and decomposed into BaSiO 3 , BaCuSi 2 O 6 , and SiO 2 when calcined at 1200°C. The relationships between the crystal structure and microwave dielectric properties of M CuSi 4 O 10 ceramics were revealed based on the Rietveld refinement and P‐V‐L complex chemical bond theory. The dielectric constant ( ε r ) decreased linearly with decreasing total bond susceptibility and ionic polarizability. Quality factor ( Q  ×  f ) was closely dependent on bond strength and lattice energy. The temperature coefficient of resonant frequency ( τ f ) was controlled by the stability of [CuO 4 ] 6− plane in M CuSi 4 O 10 . Optimum microwave dielectric properties were obtained for SrCuSi 4 O 10 when sintered at 1100°C for 3 hours with a ε r of 5.59, a Q  ×  f value of 82 252 GHz, and a τ f of −41.34 ppm/°C. Thus, SrCuSi 4 O 10 is a good candidate for millimeter‐wave devices.