Stress-Induced Nuclear Quadrupole Splittings in MgO: ${\mathrm{Mn}}^{2+}$ and Ca${\mathrm{F}}_2$: ${\mathrm{Eu}}^{2+}$

Stress-induced nuclear quadrupolar splittings are reported for ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Eu}}^{2+}$ in MgO and Ca${\mathrm{F}}_2$, respectively, using ENDOR techniques. The magnitude of all observed splittings are shown to be in agreement with point-charge estimates, in the absence of any correction for the difference between local and bulk compressibilities. An overlap contribution to the pressure-induced electric field gradient at the nucleus is calculated, and shown to be a factor of 2 smaller than the point-charge contribution. A pressure-induced dipolar contribution, appropriate to Ca${\mathrm{F}}_2$ stressed along a [111] direction, though calculated to be large (twice the point-charge value), is shown to be absent experimentally.