Measurement of quadrupole interactions in La_1-xSr _xCoO₃ perovskites using TDPAC technique

The Perturbed Angular Correlation (PAC) technique was used to study the quadrupole interactions in the La_1-x-Sr_xCoO₃ (0 ≤ x ≤ 0.08) perovskites using ¹¹¹Cd and ¹⁸¹Ta probes. The radioactive parent nuclei ¹¹¹In and ¹⁸¹Hf were introduced in the oxide lattice through chemical process during sample preparation and found to occupy only Co sites. The measurements cover a temperature range from 10 to 1150 K except the pure LaCoO₃ for which an additional measurement was made at 4.2 K. The measured quadrupole frequencies were found to decrease linearly with increasing temperature as well as with increasing Sr concentration. Temperature dependence of quadrupole frequency in the pure LaCoO₃ shows small discontinuities around 70-90 K and 500-600 K which have been atributed to thermally activated spin state transitions, from the low-spin (LS) ground state electronic configuration of Co⁺³ ion to the intermediate-spin (IS) state and from intermediate-spin (IS) state to high-spin (HS) state respectively, observed in some recent studies.