High-temperature phase transitions and low-temperature magnetic ordering inSrRuO3andCaRuO3ceramics studied using perturbed-angular-correlation spectroscopy

Perturbed-angular-correlation (PAC) spectroscopy was used to measure nuclear-electric-quadrupole interactions in the orthorhombically-distorted perovskites ${\mathrm{SrRuO}}_3$ and ${\mathrm{CaRuO}}_3$ over temperatures ranging from laboratory to very high temperatures. At 77 K, PAC spectroscopy was used to measure combined electric-quadrupole and magnetic-dipole interactions in magnetically ordered ${\mathrm{SrRuO}}_3$ and pure electric-quadrupole interactions in paramagnetic ${\mathrm{CaRuO}}_3$. The ${}_{}{}^{111}{}_{}{}^{}\to _{}^{111}{}_{}{}^{}$Cd PAC probe was used for these measurements, and it substituted into the Ru site in ${\mathrm{SrRuO}}_3$ and very likely into the Ru site in ${\mathrm{CaRuO}}_3$. The temperature dependence of the electric-field-gradient (EFG) parameters for ${\mathrm{SrRuO}}_3$ indicates the onset of a structural phase transition at approximately 800 K. The presence of this transition indicates that the laboratory-temperature structure of ${\mathrm{SrRuO}}_3$ has lower-than-cubic symmetry. At very high temperatures >1600 K, the structure of ${\mathrm{CaRuO}}_3$, as given by the EFG parameters, becomes very similar to the laboratory-temperature structure of ${\mathrm{SrRuO}}_3$. At 77 K in ${\mathrm{SrRuO}}_3$, the measured Ru-site supertransferred hyperfine field is 39±3 kOe. Using ${}_{}{}^{99}{}_{}{}^{}\mathrm{Ru}$ and ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer-effect information and other ${}_{}{}^{111}{}_{}{}^{}\to _{}^{111}{}_{}{}^{}$Cd PAC measurements, the magnetic hyperfine fields at the Ru site in ${\mathrm{SrRuO}}_3$ and at the Fe site in ${\mathrm{PrFeO}}_3$ are compared.