The effects of double-site yttria-doping on the structures and dielectric properties of (Ca,Sr)_z(Zr,Ti)O_3-d perovskite ceramics

Double-site yttria-doped (Ca,Sr)(z)(Zr,Ti)O3-delta (CSZTY) ceramics were synthesized using the solid-state reaction method. The correlation among the crystal structure, microstructure and microwave dielectric properties was investigated. Their structures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. CSZTY ceramics have a perovskite structure with coexisting orthorhombic and cubic phases; the main phase is the orthorhombic Pnma phase. Rietveld refinement, atomic-resolved high angle annular dark field (HAADF) STEM images and energy dispersive spectroscopy (EDS) for elemental mapping revealed that Y3+ cations occupy both A and B-sites in the perovskite structure (ABO(3)). Upon increasing Y3+ cations distributed on A and B-sites in CSZT ceramics, the factor of tolerance t decreases and the tilting angle of BO6 octahedra and the unit-cell volume increase. Superlattice reflections appearing along the [100](c), [110](c) and [012](c) zone axes are observed in the selected area electron diffraction (SAED) patterns as a result of cell doubling caused by the octahedral tilt transitions. Raman spectra show that upon increasing the doping amount of yttria, before and after 450 cm(-1), the frequencies of some vibrational modes correlated with B ion movement in the BO6 octahedron blue shift and red shift, respectively. Upon increasing the octahedral tilting angle, the polarizability of the ions produces corresponding changes, the dielectric constant epsilon(r) decreases, the value of Q x f increases, and the temperature coefficient of dielectric permittivity tau(c) increases while the resonant frequency temperature coefficient tau(f) decreases. At x = 0.15, the CSZTY ceramics show optimized microwave dielectric properties: epsilon(r) = 29.8, Q x f = 23 528 GHz, tau(c) = 0.50 ppm degrees C-1, and tau(f) = -4.25 ppm degrees C-1. This work provides a method to optimize the microwave dielectric properties of perovskite structure materials.