Partha Sarathi Ghosh

Molecular dynamics simulations utilizing newly developed Am ³⁺ –O ²⁻ interatomic potential models predict the phase stability and thermophysical properties of hexagonal/cubic Am ₂ O ₃ , AmO _{2− x} and Pu _{1− y} Am _y O _{2− x} MOX in the 300–3000 K temperature range.

Body-centered cubic (BCC) TixWTaVCr multi-principal element alloys (MPEAs) has indicated improved strength, hardness, and oxidation resistance at high temperatures compared to several W-rich and WTaVCr MPEAs, and eventually suggest future applications in high-temperature and nuclear domains. However, defect properties of MPEAs are also important governing factors in deciding the applicability of MPEAs in radiation atmospheres. The present study investigates the effect of Ti on the energetics of vacancy defect formation and migration in TaWVCr BCC MPEAs using first-principles calculations. The defect energetics of five Ta30W30V20Cr20, Ta30W30Ti20V20, Ta30W30Cr20V10Ti10, Ta30W30Ti20V10Cr10, and Ta30W30V20Cr10Ti10 MPEA are studied. The average defect formation energy in Ta30W30Cr20V10Ti10 and Ta30W30V20Cr10Ti10 MPEAs only differs by 0.08 and 0.20 eV, respectively, compared to Ta30W30V20Cr20. The Ti and Ta atoms undergo the largest relaxation in the first nearest neighbour (NN) shell of the deleted lattice atom. In line with the decreasing trend of average vacancy formation energy as the number of Ta and Ti atoms in the first NN shell grows, the longest relaxation distance of Ta and Ti aids in lowering the energy of the defective system. In Ta30W30V20Cr20, vacancy migration barriers of Ta are lowest, which is consistent with the previous study. However, the easy exchange between Ta and vacancy sites is impacted by the presence of Ti atoms in quinary MPEAs. An overall increase in Ta migration barriers in quinary MPEAs is observed compared to that of Ta30W30V20Cr20. Contrarily, the vacancy migration barrier is lowest for Ti among all elements in quinary MPEAs, consistent with a 0.2-0.3 eV migration barrier of BCC Ti, leading to a non-Arrhenius self-diffusivity characteristic.

A new interatomic potential for NpO ₂ is developed which predicts experimental melting temperature with reasonable accuracy. Thermal properties of Np-MOX is also predicted as a function of temperature and hyper/hypostoichiometry.

Hybrid organic-inorganic perovskites are famous for the diversity of their chemical compositions, phases, phase transitions, and associated physical properties. We use a combination of experimental and computational techniques to reveal a strong coupling between structure, magnetism, and spin splitting in a representative of the largest family of hybrid organic-inorganic perovskites: the formates. With the help of first-principles simulations, we find spin splitting in both conduction and valence bands of [NH2NH3]Co(HCOO)(3) induced by spin-orbit interactions, which can reach up to 14 meV. Our magnetic measurements reveal that this material exhibits canted antiferromagnetism below 15.5 K. The direction of the associated antiferromagnetic order parameter is strongly coupled with spin splitting in the centrosymmetric phase, allowing for the creation and annihilation of spin splitting through the application of a magnetic field. Furthermore, the structural phase transition to the experimentally observed polar Pna2(1) phase completely changes the aforementioned spin splitting and its coupling to magnetic degrees of freedom. This reveals that in [NH2NH3]Co(HCOO)(3), the structure and magnetism are strongly coupled to spin splitting and can be manipulated through electric and magnetic fields. We believe that our findings offer an important step toward a fundamental understanding and practical applications of materials with coupled properties.