The influence of hydrostatic pressure up to 2.5 kbar on the NQR spectrum of the ${}_{}{}^{75}{}_{}{}^{}\mathrm{As}$ nuclei in K${\mathrm{H}}_2$As${\mathrm{O}}_4$ is studied from 77 K to $T_c$. Using the disappearance of the NQR signal at $T_c$ to monitor the ferroelectric phase transition, the pressure dependence of $T_c$ was studied leading to $\frac{d{T}_c}{\mathrm{dp}}=-2.1\mathrm{}$ K/kbar. The energies of the ${\mathrm{H}}_2$As${\mathrm{O}}_4$ group tunneling and dipole-dipole interaction as functions of pressure, as well as the change in volume at the transitions, are determined.

• Received 7 July 1978

DOI:https://doi.org/10.1103/PhysRevB.19.1651