High-Permittivity and Low-Loss Microwave Dielectric Ceramics Based on (x)RE(Zn_(1/2)Ti_(1/2))O_3-(1-x)CaTiO_3 (RE = La and Nd)

摘要

Compositions based on REZn_(1/2)Ti_(1/2)O_3-CaTiO_3 (RE = La and Nd), suitable for microwave (MW) applications have been developed by systematically doping the perovskite B site with Ta_2O_5, Al_2O_3, and MgO in order to tune the temperature coefficient of the resonant frequency (τ_f) and improve the MW quality factor (Q × f_r) Optimized compositions, 0.45La(Zn_(0.395) Ti_(0.385)Ta_(0.01)Al_(0.21))O_3-0.55CaTiO_3 (LZT-CT) and 0.32Nd (Zn_(0.45)Mg_(0.05)Ti_(0.5))O_3-0.10NdA1O_3-0.58CaTiO_3 (NZT-CT) were prepared by solid-state reaction and have been characterized. X-ray diffraction (XRD) and scanning electron microscopy revealed that both compositions were single phase with a bulk microstructure composed of equiaxed grains (~10 um). Electron diffraction and XRD demonstrated that, at room temperature, LZT-CT and NZT-CT were orthorhombic with space group Pnma, consistent with an a~-a~-c~+ tilt system. Diffraction contrast transmission electron microscopy revealed a complex domain structure consisting of ferroelastic and antiphase domain boundaries. LZT-CT and NZT-CT had zero τ_f, ε_r = 49 and 44, Q × f_r = 29600 GHz (at 1.957 GHz), and 32200 GHz (at 1.971 GHz), respectively.