# The influence of NH4 doping on the elastic properties of RbH2AsO4 crystals

## TL;DR

This study explores how adding ammonium to RbH2AsO4 crystals changes their elastic and thermal properties, revealing transitions in crystal behavior with temperature and composition.

## Contribution

The paper introduces new insights into how ammonium doping alters the elastic and dynamic properties of RbH2AsO4 crystals.

## Key findings

- Ammonium doping causes a transition from ferroelectric to antiferroelectric and proton-glass behavior in RADA crystals.
- Elastic softening and increased phonon scattering are observed with higher ammonium content.
- Phonon thermal conductivity changes correlate with elastic anomalies due to structural disorder.

## Abstract

We report a systematic study of the elastic and dynamic properties of mixed Rb1-x(NH4)xH2AsO4 (RADA) crystals using high-resolution Brillouin light scattering over a broad temperature range (40–300 K). By varying the ammonium concentration, we reveal how \documentclass[12pt]{minimal}
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\begin{document}$$\:\text{N}{\text{H}}_{4}^{+}$$\end{document} substitution alters the elastic stiffness tensor, phase transition temperatures, phonon damping, and order parameter relaxation dynamics. The results show a clear evolution from ferroelectric to antiferroelectric and proton-glass behavior as the ammonium content increases. We observe enhanced elastic softening, increased phonon scattering, and reduced relaxation times with doping, indicating a growing degree of structural disorder and frustration in the hydrogen-bond network. The observed changes in phonon thermal conductivity correlate with these elastic anomalies. Our findings highlight the potential of chemical substitution in tuning the mechanical and thermal properties of hydrogen-bonded ferroelectric crystals, with implications for designing adaptive low-temperature optical and memory materials.

The online version contains supplementary material available at 10.1038/s41598-025-27078-7.