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

Ceramics in the system BaO-Li2O-Nd2O3-TiO2 (BNT-LNT) were prepared by the m ixed 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 s mall needle-like grains; the LNT samples comprised larger (6 mum) cubic gra ins. 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 b etween 10-20% LNT there was the development of the second phase. Small addi tions of LNT led to a small increase in relative permittivity, but decrease d the dielectric e-value (from the maximum of 1819 at 4 GHz). As BNT and LN T exhibit negative and positive temperature dependencies of permittivity re spectively, the addition of 10-20% LNT to BNT should yield samples with zer o 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) fo r the more conductive LNT. (C) 2000 Elsevier Science Ltd. All rights reserv ed.