Niobate Complex Perovskite Microwave Dieletric Ceramics Ba(Me1/3Nb2/3)O3 (Me= Zn, Co, Ni and Mg)

Abstract

Ba(Me1/3Nb2/3)O3 (Me=Zn, Co, Ni and Mg) ceramics were prepared using the conventional mixed oxide route; additives included Al2O3, Ga2O3, SiO2, WO3, B2O3 and V2O5. Powders were mixed, milled for 18h, calcined at 1100°C, remilled pressed into pellets at 100 MPa, sintered in air at temperatures in the range 1350-1550°C and then cooled at 360C h–1 to 5°C h–1. Products were characterised in terms of phase analysis (X-ray diffraction), microstructure (SEM and TEM) and electrical properties (relative permittivity, εr, dielectric Q value and temperature coefficient of resonant frequency,τf). The Q values of the Ba(Me1/3Nb2/3)O3 ceramics depend on the degree of cation ordering and the additives. Slow cooling leads to 1:2 ordering of the B sites and enhanced dielectric Q values. For samples cooled at 5°C h–1 after sintering the Qxf values are in the range 28000 to 98000 GHz, and are in the sequence Ba(Ni1/3Nb2/3)O3, Ba(Co1/3Nb2/3)O3, Ba(Mg1/3Nb2/3)O3 and Ba(Zn1/3Nb2/3)O3. Additions of BaO-4WO3 or V2O5 yield higher Qxf values than Al2O3. Highly ordered Ba(Zn1/3Nb2/3)O3 has a relative permittivity of 39.4, but most other Ba(Me1/3Nb2/3)O3 ceramics exhibit εr of 31-32. The temperature coefficient of resonant frequency, τf, varies from –18 ppm/°C (Ba(Ni1/3Nb2/3)O3) to +32 ppm/°C (Ba(Mg1/3Nb2/3)O3); the sintering additives (Al2O3 and BaO-4WO3) change τf by typically 10-16 ppm/°C.