High-Temperature Instability of Li- and Ta-Modified (K,Na)NbO3 Piezoceramics

Authors

  • Yongli Wang,

    Corresponding author
    1. Ceramics Laboratory, EPFL-Swiss Federal Institute of Technology, Lausanne 1015, Switzerland
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    • Current address: Ceramic Components Division, EPCOS OHG, 8530 Deutschlandsberg, Austria

  • Dragan Damjanovic,

    1. Ceramics Laboratory, EPFL-Swiss Federal Institute of Technology, Lausanne 1015, Switzerland
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    • *Member, The American Ceramic Society.

  • Naama Klein,

    1. Ceramics Laboratory, EPFL-Swiss Federal Institute of Technology, Lausanne 1015, Switzerland
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  • Nava Setter

    1. Ceramics Laboratory, EPFL-Swiss Federal Institute of Technology, Lausanne 1015, Switzerland
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    • *Member, The American Ceramic Society.


  • S. Trolier-McKinstry—contributing editor

  • The project was financed in part by the European FP6 MINUET and MIND programs.

†Author to whom correspondence should be addressed. e-mail: yongli.wang@epfl.ch

Abstract

This paper addresses the high-temperature instability of Li- and Ta-modified (K,Na)NbO3 piezoceramics. The grains with abnormal size evolve out of the fine matrix grains during high-temperature annealing. They are found to be precipitates with a tetragonal tungsten bronze structure, which result from the volatilization and segregation of the alkali metal elements. With the growth of the abnormal grains the composition of the perovskite matrix phase also changes remarkably, as has been suggested by EDX analysis (for Na) and electric measurements (for Li). These variations lead to a large increase in the tetragonal/orthorhombic phase transition temperature and appreciable variations in the dielectric, ferroelectric, and piezoelectric properties of the ceramic samples. Control of the volatilization of the alkali metal elements can efficiently depress the abnormal grain growth and the compositional segregation.

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