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Accurate determination of orientation relationships between ferroelastic domains: the tetragonal to monoclinic transition in LaNbO4 as an example.

  • Ø. Prytz (a1) and J. Taftø (a1)

Abstract

LaNbO4 crystallizes in a tetragonal high-temperature phase with space group I41/a, which transforms to a monoclinic phase upon cooling below 500 °C. The low-temperature phase has space group I2/a (C2/c) with a monoclinic angle β=94.1°. This system serves as a useful model of a ferroelastic transition of the 4/mF2/m type using the notation of Aizu [1]. This transition produces ferroelastic domains, the boundaries between which are parallel to the monoclinic b-axis. The orientation of these boundaries relative to the monoclinic a- and c-axes has been predicted by Sapriel [2] for all 94 ferroelastic species, and calculations specifically for the LaNbO4 system have been presented by Jian and Wayman [3].

We present an accurate determination of the boundary orientation in LaNbO4 using selected area electron diffraction. The boundary planes are parallel to the (2 0 –5.10)/(5.10 0 2) planes of the two domains, as opposed to the predictions of Jian and Wayman which indicate that the domain boundaries should be oriented parallel to the (2 0 -4.04)/(4.04 0 2) planes. Our experimental results are in good agreement with the results of a previous study [4].

Furthermore, we present a simple geometric model for calculating the boundary orientation based only on the unit cell parameters of the monoclinic phase. This model gives a boundary orientation in excellent agreement with our experimental determination.

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References

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[1] Aizu, K., Phys. Rev. B 2, 754772 (1970).
[2] Sapriel, J., Phys. Rev. B 12, 51285140 (1975).
[3] Jian, L. and Wayman, C. M., J. Am. Ceram. Soc. 79, 16421648 (1996).
[4] Tsunekawa, S. and Takei, H., Phys. Stat. Sol. (a) 50, 695702 (1978).
[5] Aizu, K., J. Phys. Soc. Japan 28, 706716 (1970).
[6] Schlenker, J. L., Gibbs, G. V. and Boisen, M. B. Jr, Acta Cryst. A34, 5254 (1978).
[7] David, W. I. F., Mater. Res. Bull. 18, 749756 (1983).
[8] Tanaka, M., Saito, R. and Watanabe, D., Acta Cryst. A36, 350352 (1980).
[9] Prytz, O. and Tafto, J., Acta Mat. 53, 297302 (2005)

Accurate determination of orientation relationships between ferroelastic domains: the tetragonal to monoclinic transition in LaNbO4 as an example.

  • Ø. Prytz (a1) and J. Taftø (a1)

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