Thermal and mechanical properties of LaNbO4-based ceramics |
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Authors: | Tommy Mokkelbost Hilde Lea Lein Per Erik Vullum Randi Holmestad Tor Grande Mari-Ann Einarsrud |
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Affiliation: | aDepartment of Materials Science and Engineering, Norwegian University of Science and Technology, N-7491 Trondheim, Norway;bDepartment of Physics, Norwegian University of Science and Technology, N-7491 Trondheim, Norway |
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Abstract: | Thermal and mechanical properties of polycrystalline La1−xAxNbO4 (x = 0, 0.005, 0.02 and A = Ca, Sr and Ba) are reported. The materials possess a ferroelastic to paraelastic phase transition close to 500 °C, and the linear thermal expansion is significantly lower ( 8.6 ± 0.5 × 10−6 °C−1) for the paraelastic phase compared to the ferroelastic phase ( 15 ± 3 × 10−6 °C−1). The hardness was significantly higher for acceptor doped materials ( 6 GPa) compared to pure LaNbO4 ( 3 GPa) due to a significantly smaller average grain size. The fracture toughness of La0.98Sr0.02NbO4, measured by single edge V-notched beam method, was 1.7 ± 0.2 MPa m1/2 independent of temperature up to 600 °C. The ferroelastic properties of the materials were confirmed by non-linear relationships between stress and strain during compression/decompression, a remnant strain after decompression and the presence of ferroelastic domains. The mechanical properties of LaNbO4-based materials are discussed with focus on ferroelasticity, microcracking due to crystallographic anisotropy and pinning of ferroelastic domain boundaries. |
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Keywords: | C Mechanical properties D Niobates |
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