Journal of Materials Research

Articles

Structure and Microwave Dielectric Properties of Ca1−xYxTi1−xAlxO3 (CYTA) Ceramics

Antonio Feteiraa1 c1, Derek C. Sinclaira1 and Michael T. Lanagana2

a1 Department of Engineering Materials, The University of Sheffield, Sheffield S1 3JD, United Kingdom

a2 Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802

Abstract

The structure and dielectric properties of Ca1−xYxTi1−xAlxO3 (CYTA) ceramics prepared by the mixed-oxide route have been investigated. CYTA forms a complete solid solution with an orthorhombic perovskite structure. Residual Y4Al2O9 and Y3Al5O12 resulting from incomplete reaction are observed for ≥ 0.9. Scanning electron microscopy shows that CYTA ceramics exhibit uniform microstructures, with an average grain size that decreases from ∼200 μm at x = 0 to ∼10 μm at x = 1.0. Transmission electron microscopy of CYTA (x = 0.3) ceramics reveals the presence of ferroelastic domains, and electron-diffraction patterns are indexed on the Pnma space group, consistent with an a+bb octahedral tilted structure. The relative permittivity, ϵr, decreases continuously from 170 to 12, while the microwave quality factor, Q·fr, increases from 10,000 to 12,000 GHz, for x = 0 and 1, respectively. CYTA (x = 0.30) ceramics exhibit ϵr ∼ 38, Q·fr of ∼14,212 GHz, and a temperature coefficient of resonance frequency, τf, of −14 ppm/°C. Small additions of acceptor (0.3 wt% ZnO) or donor (1 wt% Nb2O5) dopants decrease Q·fr by ∼20–30%, respectively.

(Received February 07 2005)

(Accepted April 27 2005)

Key Words:

  • Dielectric properties;
  • Microstructure;
  • Transmission electron microscopy (TEM)

Correspondence:

c1 Address all correspondence to this author. e-mail: a.feteira@sheffield.ac.uk

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