Ph. D. Thesis Colloquium
Name: Mr. Swapnil Shukla
Research Supervisor: Prof. D. D. Sarma
Title: Structure-property relationships in hybrid perovskites and related materials
Date and Time: Tuesday, 29th September at 04:00 p.m.
Venue: Rajarshi Bhattacharyya Memorial Lecture Hall, Chemical Sciences Building
Abstract:
The rational design and synthesis of materials with desirable functionalities have long been active areas of research in materials science.[1] One of the central challenges in the field is to understand how the structural arrangement in a material influences its macroscopic physical properties.[2] Hybrid organic-inorganic perovskites have been a versatile platform for investigating these structure-property relationships, due to their highly tunable crystal structures and strong coupling between structural, electronic, and optical degrees of freedom.[3-6] In this thesis, we explore how microscopic structural degrees of freedom, such as strain, octahedral tilting and off centring distortions control the macroscopic optoelectronic response of hybrid organic-inorganic perovskites and related layered magnets.
We present a spatially resolved, micro-diffraction study tracking the tetragonal-to-orthorhombic phase transition in MAPbI3 single crystals at a few micron resolution. By monitoring the individual phases across different spatial points and successive thermal cycles, we uncover how strain and domain distribution control the evolution of local phase fractions. [7] We then turn to a second structural degree of freedom, i.e., local distortion, in the less- explored germanium-based hybrid perovskites, AGeI3 (A = Cs, MA, and FA), focusing on the interplay between cation off-centering and octahedral tilting. Previous studies have often treated these modes as competing structural distortions, with the presence of one considered to preclude the other. Here we investigate the structural phase transitions in these materials.[8][9] We extend this structure-property framework to low-dimensional magnetic perovskites, where local octahedral distortions govern the optical response and provide a pathway for coupling to the magnetic order of the lattice. Using (BA)2MnCl4 as a model system, we investigate how Cu incorporation modifies spin and Laporte forbidden Mn-emission and magnetic properties of the doped system.[10] Finally, we extend our focus to a broader class of two-dimensional van der Waals magnets, where we use resonant inelastic X-ray scattering (RIXS) to probe the origin of the low-energy optical excitations and their coupling to the magnetic ground state in CrPS4.[11]
References:
[1] Olson, G. B. Designing a New Material World. Science 2000, 288, 993–998. https://doi.org/10.1126/science.288.5468.993
[2] Cheng, M.; Fu, C. L.; Okabe, R.; et al. Artificial Intelligence-Driven Approaches for Materials Design and Discovery. Nat. Mater. 2026, 25, 174–190. https://doi.org/10.1038/s41563-025-02403-7
[3] Pariari, D.; et al Non-monotonic Thermal Conductivity of FAx MA1-xPbI3 Achieving Ultralow Values: The Role of Anharmonic Low Energy Rotation of Organic Moieties. ACS Energy Lett. 2024, 9 (5), 2128–2136. https://doi.org/10.1021/acsenergylett.4c00047
[4] K. Mukhuti, S. Kundu, D. Pariari, D. Kalauni, A. Mohanty, A. Bajaj, D. D. Sarma, and B. Bansal, “Evidence of Athermal Metastable Phase in a Halide Perovskite: Optically Tracked Thermal-Breach Memory,” Phys. Rev. Lett. 134, 076901 (2025). https://doi.org/10.1103/PhysRevLett.134.076901
[5] Pariari, D.; et al Realizing the Lowest Bandgap and Exciton Binding Energy in a Two-Dimensional Lead Halide System. J. Am. Chem. Soc. 2023, 145 (29), 15896–15905. https://doi.org/10.1021/jacs.3c03300
[6] Guha, S.; Bera, S.; Garai, A.; Sarma, D. D.; Pradhan, N.; Acharya, S. Deriving Chiroptical Properties from Intrinsically Achiral Building Blocks of One-Dimensional CsPbBr3 Perovskite Nanowires. J. Am. Chem. Soc. 2024, 146 (49), 33883–33892. https://doi.org/10.1021/jacs.4c12490
[7] Shukla, S.; Nan, J.; Ursby, T.; Karis, O.; Sarma, D. D. Unusual Disentanglement of Nucleation and Growth of the Orthorhombic Phase in MAPbI3. Manuscript to be submitted
[8] Shukla, S.; Swain, D.; Mukherjee, P.; Ghosh, M.; Singh, A.; Sarma, D. D. Temperature-Dependent Structural and Optical Properties of CsGeI3. Chem. Mater. 2026, 38, 4481–4488. https://doi.org/10.1021/acs.chemmater.5c03103
[9] Shukla, S et.al. (manuscript under preparation.)
[10] Shukla, S et.al. (manuscript under preparation.)
[11] Shukla, S et.al. (manuscript under preparation.)