High-Pressure Refractive Indices of NaCl, KCl, CaO, SrO, and MgO Reveal the Dependence of Anion Polarizability on Coordination Number and Bond Length
Abstract
Several alkali chlorides and alkaline-earth oxides adopt the B1 structure at ambient conditions and transform to B2 under compression, allowing to change coordination number and cation-anion distance independently across chemically distinct hosts. The change in anion polarizability under high pressure dominates the optical response of these prototypical ionic solids, yet its dependence on local structure and cation chemistry remains experimentally unconstrained at high pressure. Here we report refractive indices of NaCl, KCl, CaO, and SrO to ~100, ~100, ~120, and ~60 GPa, each in both the B1 and B2 structures, complemented by published MgO-B1 indices to 140 GPa and DFT calculations. Lorentz-Lorenz analysis yields pressure-independent strain polarizability parameters Λ ranging from 0.34±0.05 for KCl-B1 to 1.57±0.02 for MgO-B2. Our results establish coordination number and cation-anion distance as separable predictors of anion polarizability in both B1 and B2 structures. Increasing anion coordination from six to eight at fixed cation-anion distance lowers the polarizability of both Cl− and O2− by ~0.34-0.40 mathringA3 and ~0.38-0.47 mathringA3 respectively. Our results suggest that the polarizability of O2− is transferable to within ~0.06 mathringA3 between MgO-B1 and CaO-B1 at fixed cation-anion distance, and that this transferability possibly extends to SrO-B1 and the B2 oxides. In contrast, the polarizability of Cl− is not transferable between NaCl-B2 and KCl-B2: the difference between them varies with cation-anion distance, from ~0.2 mathringA3 at 2.65 mathringA to 0 at ~2.5 mathringA. The results show that the change of the strain polarizability parameters across the B1-B2 transition is governed by the decreasing and increasing sensitivities of O2− and Cl− polarizabilities to densification, respectively.
Related
- Determination of fundamental properties of nitrogen from first principles. III. Temperature and frequency dependence of the molecular polarizability and magnetic susceptibility
- Temperature Dependence of the Refractive Index for AlAsGaSb
- Temperature dependence of the Casimir pressure on two graphene sheets placed on a substrate
- Pressure induced structural transitions, coordination crossover, and optoelectronic response in divalent metavanadate CaV2O6
- Diffusion of atoms produced by photodissociation in an I 2 vapour: pressure dependence of surface recombination and a correction of the decay time of the fundamental mode
BibTeX
@misc{solovev2026highpressure,
title = {{High-Pressure Refractive Indices of NaCl, KCl, CaO, SrO, and MgO Reveal the Dependence of Anion Polarizability on Coordination Number and Bond Length}},
author = {Konstantin Solovev and Xiangdong Li and Björn Winkler and Sergio Speziale and Sergey S. Lobanov},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.17290},
eprint = {2609.17290},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.17290},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - High-Pressure Refractive Indices of NaCl, KCl, CaO, SrO, and MgO Reveal the Dependence of Anion Polarizability on Coordination Number and Bond Length
AU - Konstantin Solovev
AU - Xiangdong Li
AU - Björn Winkler
AU - Sergio Speziale
AU - Sergey S. Lobanov
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2609.17290
UR - https://arxiv.org/abs/2609.17290
AB - Several alkali chlorides and alkaline-earth oxides adopt the B1 structure at ambient conditions and transform to B2 under compression, allowing to change coordination number and cation-anion distance independently across chemically distinct hosts. The change in anion polarizability under high pressure dominates the optical response of these prototypical ionic solids, yet its dependence on local structure and cation chemistry remains experimentally unconstrained at high pressure. Here we report refractive indices of NaCl, KCl, CaO, and SrO to ~100, ~100, ~120, and ~60 GPa, each in both the B1 and B2 structures, complemented by published MgO-B1 indices to 140 GPa and DFT calculations. Lorentz-Lorenz analysis yields pressure-independent strain polarizability parameters Λ ranging from 0.34±0.05 for KCl-B1 to 1.57±0.02 for MgO-B2. Our results establish coordination number and cation-anion distance as separable predictors of anion polarizability in both B1 and B2 structures. Increasing anion coordination from six to eight at fixed cation-anion distance lowers the polarizability of both Cl^− and O^2− by ~0.34-0.40 mathringA^3 and ~0.38-0.47 mathringA^3 respectively. Our results suggest that the polarizability of O^2− is transferable to within ~0.06 mathringA^3 between MgO-B1 and CaO-B1 at fixed cation-anion distance, and that this transferability possibly extends to SrO-B1 and the B2 oxides. In contrast, the polarizability of Cl^− is not transferable between NaCl-B2 and KCl-B2: the difference between them varies with cation-anion distance, from ~0.2 mathringA^3 at 2.65 mathringA to 0 at ~2.5 mathringA. The results show that the change of the strain polarizability parameters across the B1-B2 transition is governed by the decreasing and increasing sensitivities of O^2− and Cl^− polarizabilities to densification, respectively.
ER -