Pressure-induced phase transition on layered HgPSe3 revealed by optical and structural studies

Beatriz de Simoni^a, Robert Oliva^b, Miłosz Rybak^a, Jan Kopaczek^a, Filip Dybała^a, Zdeněk Sofer^c, Nikolas Antonatos^a, Robert Kudrawiec^a

^aWroclaw University of Science and Technology, Dept. of Semiconductor Materials Engineering, Wroclaw, Poland

^bGeosciences Barcelona (GEO3BCN), Spanish Council for Scientific Research (CSIC), Lluís Solé i Sabarís s/n, 08028 Barcelona, Spain.

^cDepartment of Inorganic Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28, Prague 6, Czech Republic

Proceedings of MATSUS Spring 2026 Conference (MATSUSSpring26)

D4 Synthesis and Integration of 2D Materials for Electronics, Photonics, and Functional Devices

Barcelona, Spain, 2026 March 23rd - 27th

Organizers: Nikolas Antonatos and Filipa M. Oliveira

Poster, Beatriz de Simoni, 867
Publication date: 15th December 2025

While other compounds in the family of two-dimensional transition metal trichalcogenides (MPX₃, where M is a transition metal and X = S or Se) have been extensively studied, primarily due to their magnetic properties, HgPSe₃ remains largely unexplored. In this study, we examine the influence of hydrostatic pressure on the optical and structural properties of layered HgPSe₃ through spectroscopic and diffraction techniques combined with first-principles calculations. From optical absorption measurements, the phase transition is evidenced at 3.6 GPa by a sudden redshift in the bandgap energy of approximately 200 meV. After the transition, a darkening in sample color is observed, and a reduction in the slope of the absorption coefficient suggests a transition from quasi-direct to indirect bandgap. The evolution of the lattice parameters extracted from powder X-ray diffraction measurements indicates that the compound undergoes a structural phase transition starting at 3.8 GPa from the ambient pressure monoclinic phase (space group C2/c) [1] to a high-pressure triclinic phase, once the lattice angles 𝛼 and 𝛾 start to deviate from 90°. Birch–Murnaghan fits give an experimental bulk modulus of B₀ = 29.7 GPa, in very good agreement with the theoretical value of B₀ = 28.1 GPa, demonstrating that this compound is softer than other Se-based van der Waals crystals [2-5]. Experimental pressure coefficients are obtained and compared with theoretical predictions. Our findings not only shed light on the high-pressure phase evolution of HgPSe₃ but also points to promising routes for engineering tunable van der Waals–based functionalities.

References:

[1] Jandali, M. Z.; Eulenberger, G.; Hahn, H. Z. Die Kristallstrukturen von Hg2P2S6 und Hg2P2Se6. Anorg. Allg. Chem. 1978, 447, 105–118.

[2] Wang, Y.; Zhou, Z.; Wen, T.; Zhou, Y.; Li, N.; Han, F.; Xiao, Y.; Chow, P.; Sun, J.; Pravica, M.; Cornelius, A. L.; Yang, W.; Zhao, Y. Pressure-Driven Cooperative Spin-Crossover, Large-Volume Collapse, and Semiconductor-to-Metal Transition in Manganese(II) Honeycomb Lattices. J. Am. Chem. Soc. 2016, 138, 15751–15757.

[3] Kao, Y.-C.; Huang, T.; Lin, D.-Y.; Huang, Y.-S.; Tiong, K.-K.; Lee, H.-Y.; Lin, J.-M.; Sheu, H.-S.; Lin, C.-M. Anomalous structural phase transition properties in ReSe2 and Au-doped ReSe. J. Chem. Phys. 2012, 137, 024509.

[4] Zhao, Z.; Zhang, H.; Yuan, H.; Wang, S.; Lin, Y.; Zeng, Q.; Xu, G.; Liu, Z.; Solanki, G. K.; Patel, K. D.; Cui, Y.; Hwang, H. Y.; Mao, W. L. Pressure induced metallization with absence of structural transition in layered molybdenum diselenide. Nat. Commun. 2015, 6, 7312.

[5] Selvi, E.; Aksoy, R.; Knudson, R.; Ma, Y. High-pressure X-ray diffraction study of tungsten diselenide. J. Phys. Chem. Solids 2008, 69, 2311–2314.

Acknowledgements:

B.d.S. acknowledges financial support from Marie Skłodowska-Curie Innovative Training Network (MSCA ITN (GA 956813)) within the Horizon 2020 Programme of the European Commission. R.O acknowledges ALBA synchrotron light source for funded experiments under proposals No. 2018093018 and 2023027486 at the BL04-MSPD beamline and support from the beamline scientist Dr. Catalin Popescu. N.A. and M.R. acknowledge funding from National Science Centre (NCN) Poland SONATA 19 Grant 2023/51/D/ST11/02588. M.R. acknowledges access to the BEM computing cluster provided by the Wroclaw Centre for Networking and Supercomputing (WCSS).Z.S. was supported by ERC-CZ program (project LL2101) from Ministry of Education Youth and Sports (MEYS) and by the project Advanced Functional Nanorobots (reg. No. CZ.02.1.01/0.0/0.0/15_003/0000444 financed by the EFRR).

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