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The effect of Cr and La on MgTiO3 and MgTiO3–CaTiO3 microwave dielectric ceramics

Published online by Cambridge University Press:  31 January 2011

V. M. Ferreira ,
F. Azough ,
R. Freer  and
J. L. Baptista
V. M. Ferreira
Affiliation:
Departamento de Engenharia Ceramica e Vidro, Universidade de Aveiro, 3800 Aveiro, Portugal
F. Azough
Affiliation:
Manchester Materials Science Centre, University of Manchester/UMIST, Manchester M1 7HS, United Kingdom
R. Freer
Affiliation:
Manchester Materials Science Centre, University of Manchester/UMIST, Manchester M1 7HS, United Kingdom
J. L. Baptista
Affiliation:
Departamento de Engenharia Ceramica e Vidro, Universidade de Aveiro, 3800 Aveiro, Portugal
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Abstract

Magnesium titanate and MgTiO3–CaTiO3 ceramics were prepared by a chemical (Pechini) route and classical mixed oxide route. Selected specimens were doped with Cr or La. Specimens were sintered at 1350 °C and 1400 °C. Microstructures were examined by optical microscopy, scanning electron microscopy, and transmission electron microscopy. Dielectric properties were determined at 8 GHz by the Hakki and Coleman method. The highest Q values were obtained for undoped, chemically prepared MgTiO3 (20800); any dopants caused the Q value to be degraded. Additions of small amounts of Cr (≤1 mol %) to mixed oxide magnesium titanate increased the density to 97.1% theoretical, and increased the Q value (from 7000) to 13,000. Additions of La led to the formation of La2Ti2O7 second phase and reduction in the Q value for both materials. Both Cr and La acted as effective sintering aids, increasing density (to a maximum of 99% theoretical for 1% mol La in chemically prepared samples) and relative permittivity (to 18.1 for the same specimens). The relative permittivity of MgTiO3–CaTiO3 ceramics increased with calcium content, but the corresponding Q values decreased (∈r = 19.9, Q = 8500 for Mg:Ca = 94: 6). Small additions of La to Mg–Ca titanates enhanced the dielectric Q values but decreased the relative permittivities.

Type
Articles
Information
Journal of Materials Research , Volume 12 , Issue 12 , December 1997 , pp. 3293 - 3299
Copyright
Copyright © Materials Research Society 1997

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