Structural Phase Transition and Thermochromism in Sn(IV) Halide Perovskites

Vishwajith Nagale Srikanth^a, Shubhankar Maiti^b, Ajay Prasad^a, Digvijay Singh^c, Khyati Anand^a, Prashurya Mudoi^a, Pradip Chakraborty^b, Pratap Vishnoi^a

^aNew Chemistry Unit, International Centre for Materials Science and School of Advanced Materials, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore-560064, India

^bDepartment of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India.

^cDepartment of Materials Engineering, Indian Institute of Science Bangalore, Bengaluru, India.

Proceedings of MATSUS Fall 2026 Conference (MATSUSFall26)

B1 Fundamentals and Emerging Phenomena in Halide Perovskites

Palma, Spain, 2026 October 26th - 30th

Organizers: Sascha Feldmann, Paulina Plochocka and Alexander Urban

Poster, Vishwajith Nagale Srikanth, 475
Publication date: 22nd July 2026

Vacancy-ordered Sn(IV) halide double perovskites are promising lead-free semiconductors for thermoresponsive materials, optical switching, and energy storage. They demonstrate structural robustness while retaining compositional tunability. It is important to understand how phase transitions, bandgap, and luminescence behaviour of these compounds change as the halide varies. This work explores two families of vacancy-ordered Sn(IV) halide perovskites: the hybrid variants, (TMA)₂SnX₆ (TMA = tetramethylammonium; X = Cl, Br, I) and the all-inorganic mixed-halides, K₂SnCl_6-xBr_x. (TMA)₂SnX₆ crystallize in the cubic Fd-3c structure at room temperature and undergo reversible transitions to the higher-symmetry cubic Fm-3m phase at elevated temperatures. The transition temperature can be tuned by the choice of halide ligand. Systematic halide substitution enables wide band-gap tunability from the ultraviolet to the near-infrared region, with (TMA)₂SnI₆ exhibiting a narrow band gap of 1.12 eV, highlighting its potential for solar-energy harvesting.[1]

In the case of K₂SnCl_6-xBr_x, progressive substitution of Cl by Br increases the cuboctahedral cavity size, enabling a continuous increase in the phase-transition temperature to the cubic phase from 262 K to 399 K. Notably, the transition is accompanied by pronounced and reversible thermochromism, which is visually distinguishable in K₂SnCl_1.03Br_4.97 from colourless at 300 K to bright yellow at 360 K. Further, Sb(III) cation incorporation induces p-type doping and activates a broad self-trapped excitonic (STE) orange photoluminescence at low temperatures in otherwise non-emissive K₂SnCl_6-xBr_x compounds. Raman spectroscopy and solid-state NMR measurements reveal short-range structural disorder associated with halide mixing while confirming the absence of macroscopic phase segregation. Together, these results demonstrate that vacancy-ordered Sn(IV) halide perovskites provide a highly tunable platform for composition-driven control of structural phase transitions,[2] thermochromism, and optoelectronic properties, offering new opportunities for the rational design of functional lead-free semiconductor materials.

References:

[1] N. S. Vishwajith, A. J. Prasad, D. N. Singh and P. Vishnoi, Chemistry An Asian Journal, 2025, 20, e202401483.

[2] R. Chandan, N. S. Vishwajith, K. Anand, D. N. Singh and P. Vishnoi, Chemistry An Asian Journal, 2025, 20, e00762.

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