Formation of the cerium orthovanadate CeVO4 : DFT+U study

We report density functional theory calculations of the structural, electronic, and thermodynamic properties of cerium orthovanadate (CeVO4) employing the local density approximation (LDA), generalized gradient approximation (GGA-PBE), LDA+U, and GGA-PBE+U functionals. The LDA+U, GGA-PBE+U, LDA, and GGA-PBE equilibrium volumes deviate by -2.4%, +3.6%, -7.4%, and -0.8%, respectively, from experimental results. DFT+U (DFT) predicts an antiferromagnetic (ferromagnetic) insulating (metallic) ground state, which is in agreement with experimental observations. DFT+U yields Ce and V ions in the III+ and V+ oxidation state, respectively. CeVO4 can be obtained by the reaction between Ce2O3 and V2O5 [1/2Ce(2)O(3)(s)+1/2V(2)O(5)(s)-> CeVO4(s)] under an inert atmosphere, which is described as exoenergetic (parallel to Delta H-0 parallel to=1.6-1.8 eV) by all functionals. The reaction 1/2Ce(2)O(3)(s)+1/2V(2)O(5)(s)-> CeO2(s)+VO2(s) is exoenergetic with parallel to Delta H-0 parallel to=0.75, 0.25, 1.70, and 1.24 eV for LDA+U, GGA-PBE+U, LDA, and GGA-PBE, respectively. Hence, VV+ is more easily reduced to VIV+ than CeIV+ to CeIII+, but the difference is small as obtained with DFT+U, PBE+U, in particular. The variation of this reaction energy is due to the different performance of the various approaches for the description of the change in oxidation state of cerium, IV+ to III+ [J. L. F. Da Silva , Phys. Rev. B 75, 045121 (2007)]. The small difference between the V-V and Ce-IV reducibilities may have consequences for the use of CeO2 as support of V2O5 catalysts in selective oxidation.