The energetics of La 4 LiAuO 8
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e energetics of La4LiAuO8 Tori Z. Forbesa) Peter A. Rock Thermochemistry Laboratory and NEAT ORU (Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit), University of California, Davis, California 95616
Joshua A. Kurzman Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106
Ram Seshadri Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106; and Materials Department and Materials Research Laboratory, University of California, Santa Barbara, California 93106
Alexandra Navrotskyb) Peter A. Rock Thermochemistry Laboratory and NEAT ORU (Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit), University of California, Davis, California 95616 (Received 14 January 2011; accepted 11 March 2011)
La4LiAuO8 is a stable Au3+ oxide that was recently examined as a possible model compound for the role of Au3+ in heterogeneous catalysis. Due to the paucity of thermodynamic data, the energetics of La4LiAuO8 and its likely decomposition product, LiLaO2, were investigated. The DHfox, of La4LiAuO8 and LaLiO2 are both exothermic at 187.7 6 5.8 and 41.4 6 9.6 kJ/mol, respectively. From the thermodynamic data, the decomposition temperature of La4LiAuO8 was calculated as either 979 6 95 or 1331 6 43 °C for the formation of LiLaO2 or Li2O, respectively. Thus, LiLaO2 is the expected decomposition product.
Present address: Department of Chemistry, University of Iowa, Iowa City, Iowa 52242. b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.87
To investigate the importance of Au3+ as a catalytic species, Kurzman et al.4 have studied CO oxidation in the presence of La4LiAuO8. Originally reported by Abbattista et al.,5 La4LiAuO8 crystallizes in an ordered variant of the Nd2CuO4 structure, containing layers of corner-connected LiO4 and AuO4 square planes separated by two fluoritetype layers of La and O. Each AuO4 moiety is isolated, which makes La4LiAuO8 an interesting model compound to investigate heterogeneous catalysis by square planar Au3+ ions. Although not an effective catalyst for the oxidation of CO, the compound is remarkably stable toward thermal decomposition, which occurs near 935 °C.4 The observed weight loss upon decomposition has been reported as 2.7%, corresponding to the formation of metallic Au and either 2 La2O3 + ½ Li2O or 1.5 La2O3 + LiLaO2.4 LiLaO2 is more likely to form than Li2O, but the results are ambiguous as only one small diffraction peak could be indexed to LaLiO2 in the decomposed material. LiLaO2 is the only binary compound in the La2O3–Li2O system that forms between 750 and 1000 °C.6 It is believed to be isomorphous to LiEuO2, but the detailed crystal structures of LiEuO2 and LiLaO2 are not known. LiLaO2 was observed as a decomposition product of Li3La(C2O4)39 H2O,7 and it has been reported as an effective catalyst for methane oxidation.8
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Ó Materials Research Society 2011
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