Crystal structure of corundum type Mg-4(Nb2-xTax)O-9 microwave dielectric ceramics with low dielectric loss

New microwave dielectric ceramics, i.e. Mg-4(Nb2-xTax)O-9 (MNT) solid solutions, were synthesized and their microwave dielectric properties and crystal structure were investigated in this study. From the discrete variational Xalpha (DV-Xalpha) method, it was found that the Ta-O bonds in the TaO6 octahedron become more covalent than Nb-O bonds in the NbO6 octahedron; this result leads to the decrease of the ionicity in the Ta5+ ion. The dielectric constants of MNT were slightly decreased from 12.4 to 11.5; this result might be due to the covalent interaction of Ta-O bonding. The quality factors of the samples were found to exhibit high value (Q.f = 350 000 GHz for x 2) which is comparable to those of Al2O3. (C) 2003 Elsevier Ltd. All rights reserved.