Structural phase transition and Tc distribution in Hf-doped LaMnO3 investigated using perturbed-angular-correlation spectroscopy.

Using perturbed-angular-correlation ~PAC! spectroscopy, via the Hf→Ta probe, we have measured Mn-site electric-field gradients ~EFG’s! at Ta nuclei in ceramic samples of LaMnO3. Two crystallographic phases coexist over a temperature interval of '16 K near the orthorhombic-to-rhombohedral transition at '724 K, which shows a thermal hysteresis of '1.760.2 K. Concurrently, in the two phases, we determined the temperature dependence of the EFG parameters, Vzz , h , and d , and the ratio of the probe concentrations A1 /A2. To explain the apparent coexistence of two phases in this weakly first-order transition, we present a model that assumes a spatial distribution of Tc values. This distribution could arise from a spatially nonuniform distribution of Mn ions. We show the PAC technique to be a uniquely powerful probe of local symmetries that reflect the effects of a local distribution of valences, which drive the phase transition. @S0163-1829~96!52230-7#