arXiv subjects

Swapan Pati

Publications and source records attributed to Swapan Pati.

3 recordsLinked to original sources

arXiv2026

Thermodynamic origin of medium-entropy stabilization in multicomponent rock-salt oxides

High entropy oxides are commonly associated with high configurational entropy ($\Delta S_{conf}\geq$ 1.61R) corresponding to five equimolar cations occupying a crystallographic sublattice. However, recent experimental observations indicate that medium-entropy compositions may also exhibit entropy-stabilized rock-salt phases, raising an important question regarding the minimum entropy required for phase stabilization. In this work, we employ a first-principles thermodynamic framework to investigate the stability of rock-salt oxides containing two to five principal cations components analogous to (Ni$_{0.8}$Cu$_{0.2}$)O, (Ni$_{0.6}$Cu$_{0.2}$Zn$_{0.2}$)O, (Ni$_{0.4}$Cu$_{0.2}$Zn$_{0.2}$Co$_{0.2}$)O, (Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$Co$_{0.2}$Mg$_{0.2}$)O. Density functional theory, MCSQS-based structural modeling, and finite-temperature Gibbs free-energy analysis are combined to quantify the roles of enthalpy mixing ($\Delta H_{mix}$), configurational ($\Delta S_{conf}$), vibrational ($\Delta S_{vib}$), and electronic contributions towards ($\Delta S_{elec}$) entropy change in governing phase stability. The results show that $\Delta S_{conf}$ alone is not a universal descriptor of phase stability. While the two-cation system is enthalpy-stabilized but three-, four- and five-cation systems become thermodynamically stable at high-temperature due to entropy-driven reduction of the Gibbs free energy. These findings demonstrate that single-phase rock-salt oxides are not restricted to the conventional high-entropy limit and that medium-entropy compositions can also be stabilized under suitable thermodynamic conditions.

cond-mat.mtrl-sci↗

arXiv1996

A comparative study of the phase diagrams of spin-$1 \over 2$ and spin-$1$ antiferromagnetic chains with dimerization and frustration

We use the density matrix renormalization group method to study the ground state `phase' diagram and some low-energy properties of isotropic antiferromagnetic spin-$1 \over 2$ and spin-$1$ chains with a next-nearest neighbor exchange $J_2 ~$ and an alternation $δ$ of the nearest neighbor exchanges. In the spin-$1 \over 2$ chain, the system is gapless for $δ=0$ and $J_2 < J_{2c} =0.241$, and is gapped everywhere else in the $J_2 - δ$ plane. At $J_{2c}$, for small $δ$, the gap increases as $δ^α$, where $α= 0.667 \pm 0.001$. $2J_2 + δ= 1$ is a disorder line. To the left of this line, the structure factor $S(q)$ peaks at $q_{max} = π$ (Neel `phase'), while to the right, $q_{max}$ decreases from $π$ to $π/2$ (spiral `phase') as $J_2$ increases. There is also a `$\uparrow \uparrow \downarrow \downarrow$ phase' for large values of both $J_2$ and $δ$. In the spin-$1$ case, we find a line running from a gapless point at $(J_2 , δ) = (0,0.25 \pm 0.01)$ upto a `gapless' point at $(0.73 \pm 0.005,0)$ such that the open chain ground state is four-fold degenerate below the line and is unique above it. There is a disorder line in this case also and it has the same equation as in the spin-$1 \over 2$ case, but the line ends at about $δ=0.136$. Similar to the spin-$1 \over 2$ case, to the left of this line, the peak in the structure factor is at $π$ (Neel `phase'), while to the right of the line, it is at less than $π$ (spiral `phase'). For $δ=1$, the system corresponds to a spin ladder and the system is gapped for all values of the interchain coupling for both spin-$1 \over 2$ and spin-$1$ ladders.

cond-mat↗

arXiv1995

Phase Diagram of the Spin-One Heisenberg System with Dimerization and Frustration

We use the density matrix renormalization group method to study the ground state properties of an antiferromagnetic spin-$1$ chain with a next-nearest neighbor exchange $J_2 ~$ and an alternation $δ$ of the nearest neighbor exchanges. We find a line running from a gapless point at $(J_2 , δ) = (0, 0.25 \pm 0.01)$ upto an almost gapless point at $(0.725 \pm 0.01, 0$ such that the open chain ground state is $4$-fold degenerate below the line and is unique above it. A disorder line $2 J_2 + δ= 1$ runs from $δ=0$ to about $δ=0.136$. To the left of this line, the peak in the structure factor $S(q)$ is at $π$, while to the right of the line, it is at less than $π$.

cond-mat↗