Structural evolution and microwave dielectric properties of CaTiO3-La(Mg2/3Nb1/3)O-3 ceramics

(1 - x)CaTiO3-xLa(Mg2/3Nb1/3)O-3 (CT-LMN; x = 0-1.0) solid solutions were prepared by a solid-state reaction method. A phase transition from a disordered orthorhombic (Pbnm) structure to a 1:1 ordered monoclinic (P21/n) structure was observed when x increased from 0.5 to 0.6. Some new parameters, such as ionic polarizability in a polyhedron and ionic packing fraction in a polyhedron, were defined to explain the structure-property relationships of CT-LMN ceramics based on the Rietveld refinement results. The measured dielectric constant (epsilon(r-mea)) decreased monotonically with B-site ionic polarizability in the [BO6] octahedron (alpha DT(B)/V[B]$\alpha _{\rm{D}}<^>{\rm{T}}( {\rm{B}} )/{V_{[ {\rm{B}} ]}}$) when the x value increased from 0 to 1.0. The quality factor (Qf) was dominated by the packing fraction of B-site cations in the [BO6] octahedron (PF[B]), and both presented an increasing trend. The temperature coefficient of resonant frequency (tau(f)) decreased from +588.5 to -79.7 ppm/degrees C, and it was highly correlated to the tolerance factor (t), alpha DT(B)/alpha DT(B)V[B]V[B]${{\alpha _D<^>T( {\rm{B}} )} \mathord{/ {\vphantom {{\alpha _D<^>T( {\rm{B}} )} {{V_{[ {\rm{B}} ]}}}}} \kern-\nulldelimiterspace} {{V_{[ {\rm{B}} ]}}}}$ and PF[B]. The highest Qf value is obtained at x = 1.0 when sintered at 1600 degrees C for 10 h with epsilon(r) = 23.65 +/- 0.2, Qf = 33517 +/- 2000 GHz (@7.8 GHz), and tau(f) = -79.7 +/- 2.0 ppm/degrees C. Moreover, a near-zero tau(f) value was achieved at x = 0.4 with epsilon(r) = 43.52 +/- 0.2, Qf = 17239 +/- 2000 GHz (@5.2 GHz), and tau(f) = -10.2 +/- 2.0 ppm/degrees C.