Presentation Information
[15a-W9_323-4]Thermal expansion in Cross-Coupled order parameter oxides
〇Hena Das1,2, Masaki Azuma1,2 (1.KISTEC, 2.Science Tokyo)
Keywords:
Anomalous thermal expansion,Anharmonic Grüneisen theory,Complex oxides
Phase transitions and thermal responses in Ruddlesden-Popper (A2BO4) oxides emerge from intricate couplings among structural, electronic, and magnetic order parameters. Harnessing these couplings enables the rational design of materials with tailored quantum and thermal functionalities. Here, we integrate density functional theory (DFT), molecular dynamics, and machine learning-based methods to engineer octahedral distortions governing such responses. Using Ca2RuO4 as a model system, we elucidate the microscopic mechanism underlying its colossal uniaxial negative thermal expansion (NTE) and metal-to-insulator transition [npj Comput. Mater. 11, 356 (2025), Chem. Mater. 33, 7665-7674 (2021)]. Phonons with negative Grüneisen parameters strongly coupled to elastic anisotropy and non-rigid RuO6 tilts drive this NTE through temperature-induced anharmonic lattice dynamics beyond the quasi-harmonic approximation (QHA) [npj Comput. Mater. 11, 356 (2025)]. Machine learning force-field molecular dynamics captures the interplay among octahedral rotations, tilts, and antipolar displacements, revealing actionable pathways to tune thermal and phase behavior via octahedral distortion design across layered oxide families.