Thermodynamic stabilities of LaVO3 and LaVO4 by e.m.f. methods

Pankajavalli, R.; Sreedharan, O.M.

doi:10.1016/0167-577x(95)00096-8

Cited by 13 publications

(9 citation statements)

References 10 publications

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“…Besides, the trends can be described in terms of simple variables such as the number of valence electrons and oxidation states, and explained through simple and clear solid-state physics arguments. Furthermore, the validation through DFT calculations of experimentally observed trends 17 gives hope for the reliability of the unobserved ones herein reported and opens up the path for future systematic experimental works.…”

Section: Origin Of the Trends In Formation Energiesmentioning

confidence: 52%

“…Since perovskite oxides have the same general chemical formula (ABO 3 ) and share the same BO 6 octahedral framework, there must be rational ways of visualizing the trends in their formation energies. This requires the identification of descriptors that smoothly show how different metals at different sites influence their formation energies, something available but rather scarce in the literature, 15,17 because most of the studies report data with no focus on the trends among the components of the samples. Such an insight could also open a way to rationally estimate the formation energy of perovskites that have not yet been reported experimentally or theoretically.…”

Section: Introductionmentioning

confidence: 99%

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Generalized trends in the formation energies of perovskite oxides

Zeng

Calle‐Vallejo

Mogensen

et al. 2013

Phys. Chem. Chem. Phys.

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Generalized trends in the formation energies of several families of perovskite oxides (ABO3) and plausible explanations to their existence are provided in this study through a combination of DFT calculations, solid-state physics analyses and simple physical/chemical descriptors. The studied elements at the A site of perovskites comprise rare-earth, alkaline-earth and alkaline metals, whereas 3d and 5d metals were studied at the B site. We also include ReO3-type compounds, which have the same crystal structure of cubic ABO3 perovskites except without A-site elements. From the observations we extract the following four conclusions for the perovskites studied in the present paper: for a given cation at the B site, (I) perovskites with cations of identical oxidation state at the A site possess close formation energies; and (II) perovskites with cations of different oxidation states at the A site usually have quite different but ordered formation energies. On the other hand, for a given A-site cation, (III) the formation energies of perovskites vary linearly with respect to the atomic number of the elements at the B site within the same period of the periodic table, and the slopes depend systematically on the oxidation state of the A-site cation; and (IV) the trends in formation energies of perovskites with elements from different periods at the B site depend on the oxidation state of A-site cations. Since the energetics of perovskites is shown to be the superposition of the individual contributions of their constituent oxides, the trends can be rationalized in terms of A-O and B-O interactions in the ionic crystal. These findings reveal the existence of general systematic trends in the formation energies of perovskites and provide further insight into the role of ion-ion interactions in the properties of ternary compounds.

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Section: Origin Of the Trends In Formation Energiesmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Generalized trends in the formation energies of perovskite oxides

Zeng

Calle‐Vallejo

Mogensen

et al. 2013

Phys. Chem. Chem. Phys.

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“…All families of perovskites exhibit a systematic linear scaling between their energetics and the atomic number of M. The scaling in Figure 2 was previously revealed by experiments only for some La perovskites at 1273 K. [13] We extend this behavior to other families of perovskites, and the insight allows the following generalization: the slope of the lines is determined by the oxidation states of A and M. Therefore, these compounds could be divided into two groups: perovskites with the same oxidation state for A and M (+ III for A'MO 3 ; A' = Y, La), and perovskites in which their oxidation states differ (+ II and + IV for A''MO 3 ; A'' = Ca, Sr, and Ba). The former are more stable than the latter and their stabilities along the 3d series decrease more slowly, that is, their lines have less steep slopes.…”

mentioning

confidence: 73%

Trends in Stability of Perovskite Oxides

et al. 2010

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Perovskite oxides with general formula AMO 3 have a large variety of applications as dielectrics and piezoelectrics, [1] ferroelectrics [2] and/or ferromagnetic materials, [3] among others. Rare earth and alkaline earth metal perovskites are useful as catalysts for hydrogen generation, [4] as oxidation catalysts for hydrocarbons, [5] and as effective and inexpensive electrocatalysts for state-of-the-art fuel cells, [6] mainly due to the possibility of tuning their mixed ionic-electronic conductivity through substitution of A and M and subsequent formation of oxygen vacancies. Despite the general interest in perovskites, so far there have been no ab initio studies devoted to their formation energies, and the trends in stability are unknown.Among the available theoretical techniques to investigate perovskites, DFT is an appealing candidate, since it has proved useful for understanding metals and alloys at the atomic scale.[7] Nevertheless, the well-known shortcoming of DFT in describing strongly correlated systems has prevented its use for the estimation of properties such as band gaps and electron localization-delocalization of oxides, and there are numerous corrections. [8] Despite these limitations, Figure 1 a shows the experimental formation energies from elements and O 2 of 20 perovskites at 298 K and the corresponding standard DFT energies using the RPBE-GGA [9] exchange-correlation functional. The simulations are able to reproduce trends in the formation energies, and the calculated energies are shifted by about 0.75 eV compared to experiments. The A component is Y, La, Ca, Sr, or Ba, while M is a 3d metal from Ti to Cu. However, it is possible to combine the formation energies of these compounds with those of their sesquioxides (A 2 O 3 and M 2 O 3 ), rutile dioxides (MO 2 ), monoxides (AO and MO), and O 2 to reproduce the energetics of several reactions (Figure 1 b-d). The reactions are shown in the Supporting Information. The excellent correspondence between experiments and theory shows that DFT very accurately captures the mixing energies between oxides. The chemical reaction depicted in Figure 1 a and the way of representing its Gibbs energy, are given by Equations (1) and (2).In terms of trends the agreement is beyond the expected accuracy of DFT in general, but the shift is about 0.75 eV. We note that imitations in O 2 description by DFT are well known and some alternatives have been proposed, obtaining remarkable agreements with experiments. [8c,10] We obtain the total DFT energy of O 2 indirectly from the tabulated Gibbs energy of formation of water and from the DFT energies of H 2

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“…All families of perovskites exhibit a systematic linear scaling between their energetics and the atomic number of M. The scaling in Figure 2 was previously revealed by experiments only for some La perovskites at 1273 K 13. We extend this behavior to other families of perovskites, and the insight allows the following generalization: the slope of the lines is determined by the oxidation states of A and M. Therefore, these compounds could be divided into two groups: perovskites with the same oxidation state for A and M (+III for A′MO 3 ; A′=Y, La), and perovskites in which their oxidation states differ (+II and +IV for A′′MO 3 ; A′′=Ca, Sr, and Ba).…”

mentioning

confidence: 99%

Methylidene Rare‐Earth‐Metal Complex Mediated Transformations of CN, NN and NH Bonds: New Routes to Imido Rare‐Earth‐Metal Clusters

Hong¹,

Zhang²,

Wang³

et al. 2013

Chemistry A European J

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Three new patterns of reactivity of rare-earth metal methylidene complexes have been established and thus have resulted in access to a wide variety of imido rare-earth metal complexes [L3Ln3(μ2-Me)3(μ3-Me)(μ-NR)] (L = [PhC(NC6H3iPr2-2,6)2](-); R = Ph, Ln = Y (2 a), Lu (2 b); R = 2,6-Me2C6H3, Ln = Y (3 a), Lu (3 b); R = p-ClC6H4, Ln = Y (4 a), Lu (4 b); R = p-MeOC6H4, Ln = Y (5 a), Lu (5 b); R = Me2CHCH2CH2, Ln = Y (6 a), Lu (6 b)) and [{L3Lu3(μ2-Me)3(μ3-Me)}2(μ-NR'N)] (R' = (CH2)6 (7 b), (C6H4)2 (8 b)). Complex 2 b was treated with an excess of CO2 to give the corresponding carboxylate complex [L3Lu3(μ-η(1):η(1)-O2CCH3)3(μ-η(1):η(2)-O2C-CH3)(μ-η(1):η(1):η(2)-O2CNPh)] (9 b) easily. Complex 2 a could undergo the selective μ3-Me abstraction reaction with phenyl acetylene to give the mixed imido/alkynide complex [L3Y3(μ2-Me)3(μ3-η(1):η(1):η(3)-NPh)(μ3-C≡CPh)] (10 a) in high yield. Treatment of 2 with one equivalent of thiophenol gave the selective μ3-methyl-abstracted products [L3Ln3(μ2-Me)3(μ3-η(1):η(1):η(3)-NPh)(μ3-SPh)] (Ln = Y (11 a); Lu (11 b). All new complexes have been characterized by elemental analysis, NMR spectroscopy, and most of the structures confirmed by X-ray diffraction.

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Thermodynamic stabilities of LaVO3 and LaVO4 by e.m.f. methods

Cited by 13 publications

References 10 publications

Generalized trends in the formation energies of perovskite oxides

Generalized trends in the formation energies of perovskite oxides

Trends in Stability of Perovskite Oxides

Methylidene Rare‐Earth‐Metal Complex Mediated Transformations of CN, NN and NH Bonds: New Routes to Imido Rare‐Earth‐Metal Clusters

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