Phase transitions and optical properties of the trigonal perovskite (CH3NH3)2TeCl6

Yuhan Liu; Jeremy K. Cockcroft; Zizhen Chen; Michael A. Hayward; Paul F. Henry; Robin S. Perry; Robert G. Palgrave

doi:10.1039/D2TC02372E

Phase transitions and optical properties of the trigonal perovskite (CH₃NH₃)₂TeCl₆†

Yuhan Liu,

^a Jeremy K. Cockcroft,

^a Zizhen Chen,^b Michael A. Hayward,

^b Paul F. Henry,

^cd Robin S. Perry*^ce and Robert G. Palgrave

*^a

Author affiliations

* Corresponding authors

^a Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
E-mail: r.palgrave@ucl.ac.uk

^b Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK

^c ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK

^d Department of Chemistry, Ångström Laboratory, Box 538, 751 21, Uppsala, Sweden

^e London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK
E-mail: robin.perry@ucl.ac.uk

Abstract

Vacancy-ordered double perovskites A₂BX₆ are attracting attention due to the isolated octahedra making them an ideal playground for studying perovskite structure-property relationships. MA₂TeCl₆ single crystals have been successfully grown from solution. X-ray structure experiments as a function of temperature have demonstrated two structural phase transitions: from cubic Fm [3 with combining macron] m (high temperature, phase I) to trigonal Pm1 (intermediate temperature, phase II) at 460 K and then to trigonal P1c (low temperature, phase III) at 200 K. Intriguingly, we observe a negative thermal expansion for the c-axis in phase II believed to caused by dynamic tilting of the C–N bond in the MA⁺ ion. We have modified and extended the calculation of the Brown radii ratio in the perovskites to include hybrid A₂BX₆ compounds by selecting the shortest A–X distance for the ratio equation. We find that for ratios between 0.89 and 1.17, typically the Fm [3 with combining macron] m cubic structure is observed, while for ratios above 1.17, mostly distorted structures are found.

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Article information

DOI: https://doi.org/10.1039/D2TC02372E
Article type: Paper
Submitted: 07 Jun 2022
Accepted: 18 Jul 2022
First published: 18 Jul 2022
This article is Open Access

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J. Mater. Chem. C, 2022,10, 11938-11945

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Phase transitions and optical properties of the trigonal perovskite (CH₃NH₃)₂TeCl₆

Y. Liu, J. K. Cockcroft, Z. Chen, M. A. Hayward, P. F. Henry, R. S. Perry and R. G. Palgrave, J. Mater. Chem. C, 2022, 10, 11938 DOI: 10.1039/D2TC02372E

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Journal of Materials Chemistry C