Enthalpies of formation of ABO3 (A = Ca, Sr, Ba; B = Ti, Zr, Hf) from the binary constituent oxides have been calculated by ab initio density functional theory. The resulting values compare well with the large number of experimental determinations reported in literature. The trends in the calculated enthalpies of formation correlate with the difference in acidity between the binary constituent oxides. Density functional theory is shown to be a valuable tool that should be used routinely in thermochemical studies of inorganic compounds.
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BYThe temperature dependence of the nuclear quadrupole interaction in metals has been investigated in several recent publications. Special attention has been given to non-cubic metals where the reported measurements cover pure metals /1, 2/, alloys /3/, and dilute binary alloys /4/. The systematics emerging from these data show that the electric field gradients (EFG) follow a very simple T3'2 relation. Recently it was also shown /5/ that the EFG generated by impurity atoms diffused into cubic Ag metals also presents a T3/2 dependence. Simultaneously various theoretical models have been proposed to explain these systematics in non-cubic metals / 4 , 6 , 7/. Most of the proposed approaches suggest that the conduction electrons play an important role in the T3" behaviour. It seems then that an investigation of the temperature dependence of EFG in non-metals i s an interesting problem. of the nuclear quadrupole interaction on 181Ta in CaHfO using the time-differ-3 ential perturbed angular correlation (TDPAC) technique. was prepared following the method given in /a/: a small dry-pressed pellet made from an equimolar composition of CaO and Hf02 was fired a t 1550 OC for 6 h and allowed to cool slowly. The sample was submitted to a X-ray diffractogram which confirme& the previously measured structure /8/. The radioactivity was obtained by the reaction Hf(n,r)181Hf, where lalHf decays by p--emission populating levels of lalTa. The TDPAC experiment was performed through the 133 to 482 keV p --d cascade in lalTa measuring the interaction of the quadrupole moment of the 482 keV, I = 5/2 state, with the EFG's acting a t the Ta nuclei in the calcium hafnate.We report here the experimental determination of the temperature dependenceThe calcium hafnate 180 1) 90 000 Porto Alegre. RS, Brazil.2) Work supported in part by FINEP and CNPq.3) On a fellowship from 0 . E .A.5 physica @)
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