Temperature dependence of electric field gradient inLaCoO3 perovskite investigated by perturbed angular correlation spectroscopy

Abstract

The time differential perturbed angular correlation (TDPAC) technique wasused to study the temperature dependence of electric field gradient (EFG) inLaCoO3 perovskite using and nuclear probes. The radioactive parent nuclei111In and 181Hf were introduced into the oxide lattice through a chemical process duringsample preparation and were found to occupy only the Co sites inLaCoO3. The PACmeasurements with 111Cd and 181Ta probes were made in the temperature range of 4.2–1146 K and 4.2–1004 K,respectively. No long-range magnetic order was observed up to 4.2 K. The EFGs at111Cd and 181Ta show very similar temperature dependences. They increase slowly between 4.2 and about77 K and then decrease almost linearly with increasing temperature until about 500–600 K,where a broad peak-like structure is observed, followed by linear decrease at stillhigher temperatures. These discontinuities at about 77 K and 500–600 K havebeen interpreted as thermally activated spin state transitions from the low-spin(t2g6eg0) ground state configuration to the intermediate-spin(t2g5eg1) state and from the intermediate-spin to the high-spin(t2g4eg2) stateof the Co3+ ion, confirming previous observation in other recent studies. An indication of a Jahn–Tellerdistortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointedout.