Low-temperature sintering of temperature-stable LaNbO4 microwave dielectric ceramics

We demonstrate the correlation between sintering behavior and microstructural observations in low-temperature sintered, LaNbO4 microwave ceramics. Small CuO additions to LaNbO4 significantly lowered the sintering temperature from 1250 to 950 °C. To elucidate the sintering mechanism, the internal microstructure of the sample manipulated by a focused ion beam (FIB) was investigated using transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). LaNbO4 with 3 wt% CuO sintered at 950 °C for 2 h possessed the following excellent microwave dielectric properties: a quality factor (Qxf) of 49,000 GHz, relative dielectric constant (ɛr) of 19.5, and temperature coefficient of resonant frequency (τf) of 1 ppm/°C. The ferroelastic phase transformation was also investigated using in situ X-ray diffraction (XRD) to explain the variation of τf in low-temperature sintered LaNbO4 as a function of CuO content.