Acta Crystallographica Section B

Structural Science

Volume 58, Part 5 (October 2002)

research papers

Acta Cryst. (2002). B58, 750-759 [ doi:10.1107/S0108768102010066 ]

Structural study of the low-temperature phase of TlH₂PO₄ at 180 K

E. Álvarez-Otero, G. Madariaga, I. Peral, C. L. Folcia and S. Ríos

Abstract: The low-temperature phase of TlH₂PO₄ has been studied by X-ray diffraction. A structural model is proposed with space group P $\bar 1$ . This model is compared with the structure of the antiferroelectric phase of TlD₂PO₄ at room temperature to analyze the expected isomorphism at low temperature. Given the structural distortion of TlH₂PO₄, such isomorphism present in the common high-temperature phase is not recovered in this phase. Through the analysis of the displacements of the PO₄ groups there is some evidence that the ordering of the H atoms responsible for the appearance of antiferroelectricity seems to be incomplete. An exhaustive study of the detected ferroelastic domains is also performed.

Keywords: TlH₂PO₄; X-ray diffraction; antiferroelectricity.