Lattice thermal expansion of LaCo 1− xCu xO 3

Abstract

Lattice thermal expansion studies on LaCo 1− x Cu x O 3 ( x=0, 0.02, 0.05, 0.1, 0.3 and 0.5) were carried out by high temperature XRD from room temperature to 1173 K. A linear increase in lattice parameter was observed with increase in copper concentration indicating the substitution of copper in the lattice. The % volume thermal expansion (∇ V∗100/V) increases with temperature. As the copper concentration increases from 0.0 to 30 mol.%, the % volume thermal expansion decreases from 5.98 to 4.522. The lattice and volume thermal expansion coefficients (TEC), ᾱ a , ᾱ c , and ᾱ v averaged between 298 and 1023 K are calculated using the HTXRD data. ᾱ a, ᾱ c and ᾱ v decreased from 26.78×10 −6 to 18.27×10 −6 K −1, 27.81×10 −6 to 24.56×10 −6 K −1 and 82.45×10 −6 to 72.9×10 −6 K −1, respectively, as the copper concentration increased from 0 to 30 mol.%. The decrease in TEC with copper loading is due to the introduction of the covalent character of the Cu–O bond in the otherwise ionic nature of the La–O bond in LaCoO 3. The larger decrease in ᾱ a as compared to ᾱ c confirms the substitution of more copper in the a–b plane rather than in the c-axis.