Microwave dielectric ceramics in the system BaO-Li2O-Nd2O3-TiO2

Ceramics in the system BaO-Li2O-Nd2O3-TiO2 (BNT-LNT) were prepared by the mixed oxide route. Powders were mixed, milled, calcined and sintered at 1475 degreesC for 4 h. Fired densities decreased steadily along the series from BNT to LNT. The microstructures of samples rich in BNT were dominated by small needle-like grains; the LNT samples comprised larger (6 mum) cubic grains. X-ray diffraction showed that there was a transition from orthorhombic BNT to cubic LNT; small amounts of LNT could be accommodated in BNT, but between 10-20% LNT there was the development of the second phase. Small additions of LNT led to a small increase in relative permittivity, but decreased the dielectric e-value (from the maximum of 1819 at 4 GHz). As BNT and LNT exhibit negative and positive temperature dependencies of permittivity respectively, the addition of 10-20% LNT to BNT should yield samples with zero temperature dependence of epsilon (r) Impedance spectroscopy showed that data could only be acquired at elevated temperatures for BNT rich samples (above 500 degreesC), but at modest temperatures (less than 100 degreesC) for the more conductive LNT. (C) 2000 Elsevier Science Ltd. All rights reserved.