A neutron diffraction study of LaCoO3 in the temperature range 4.2 < T < 1248 K

The structure of LaCoO3 has been reexamined using high-intensity and high-resolution powder neutron diffraction, the latter measurements being made at 4, 71, 293, 668, 1143, and 1248 K. Only in the 668 K data is there evidence for R3 instead of R3c symmetry, found at other temperatures. Previous X-ray diffraction work suggested that the R3 space group was retained from 648 K through a first-order semiconductor-metal transition at 1210 K. The R3c cell parameters found are: a = 5.3416(1)Å, α = 60.990(1)° [4K]; a = 5.3489(1)Å, α = 60.966(1)° [71 K]; a = 5.3778(1)Å, α = 60.798(1)° [293 K]; a = 5.4355(1)Å, α = 60.599(1)° [668 K]; a = 5.5001(2)Å, α = 60.357(2)° [1143 K]; a = 5.150(2)Å, α = 60.296(2)° [1248 K]. The R3 cell parameters obtained from the 668 K data are a = 5.4354(1)Å, α = 60.599(1)°. These results are in accord with our previously reported differential thermal analysis (DTA) and electrical conductivity data and with a model based on collective 3d-electron behavior over the temperature range studied.