Phase analysis and dielectric properties of oxides obtained in the MgO-(1-x)Nb2O5-(x)Ta2O5

Citation
M. Thirumal et Ak. Ganguli, Phase analysis and dielectric properties of oxides obtained in the MgO-(1-x)Nb2O5-(x)Ta2O5, P I A S-CH, 113(5-6), 2001, pp. 603-610
Citations number
6
Categorie Soggetti
Chemistry
Journal title
PROCEEDINGS OF THE INDIAN ACADEMY OF SCIENCES-CHEMICAL SCIENCES
ISSN journal
02534134 → ACNP
Volume
113
Issue
5-6
Year of publication
2001
Pages
603 - 610
Database
ISI
SICI code
0253-4134(200110/12)113:5-6<603:PAADPO>2.0.ZU;2-8
Abstract
MgNb2-xTaxO6 (0 less than or equal to x less than or equal to 2) phases can be obtained as the major phase (75 to 90%) by solid state reactions starti ng from oxides. These oxides crystallize in the orthorhombic columbite stru cture till x = 1.75 and the tetragonal triutile structure for MgTa2O6 (x = 2.0). For all the compositions there exist secondary phases like Nb2O5 or T a2O5 in addition to the major AB(2)O(6) phase. Sintered disks (1200 degrees C) show dielectric constants varying between 14.8 and 16.0 for the entire r ange of composition at a frequency of 500 kHz. The dielectric loss is nearl y constant around 0.025 to 0.03 between 0 less than or equal to x less than or equal to 1 but increases to 0.17 for the MgTa2O6 phase (x = 2.0). Scann ing electron micrographs reveal a gradual decrease in grain size with incre ase in Ta concentration with a size of 3 micron for the x = 0 composition ( sintered at 1200 degreesC) while the x = 2 phase shows a grain size of appr oximately 0.5 microns. The microwave dielectric constant at similar to 14 G Hz is found to be 20.9 for the x = 0 composition and 17.7 for the x = 2 com position.