Magnetic Structure of CoO

The paper reports evidence that the multi-spin-axis magnetic structure proposed in 1964 by van Laar is realized in antiferromagnetic CoO. This tetragonal spin arrangement produces both the strong tetragonal and the weaker monoclinic distortion experimentally observed in this material. The monoclinic distortion is proposed to be a “monoclinic-like” distortion of the array of the oxygen atoms, comparable with the rhombohedral-like distortion of the oxygen atoms recently proposed to be present in NiO and MnO. The monoclinic-like distortion has no influence on the tetragonal magnetic structure, which is generated by a special nonadiabatic atomic-like motion of the electrons near the Fermi level. It is argued that it is this atomic-like motion that qualifies CoO to be a Mott insulator.

Vacancy defect control of colossal thermopower in FeSb2

Iron diantimonide is a material with the highest known thermoelectric power. By combining scanning transmission electron microscopic study with electronic transport neutron, X-ray scattering, and first principle calculation, we identify atomic defects that control colossal thermopower magnitude and nanoprecipitate clusters with Sb vacancy ordering, which induce additional phonon scattering and substantially reduce thermal conductivity. Defects are found to cause rather weak but important monoclinic distortion of the unit cell Pnnm → Pm. The absence of Sb along [010] for high defect concentration forms conducting path due to Fe d orbital overlap. The connection between atomic defect anisotropy and colossal thermopower in FeSb2 paves the way for the understanding and tailoring of giant thermopower in related materials.

On the lack of Monoclinic Distortion in the Insulating Regime of EuNiO3 and GdNiO3 perovskites by high-angular resolution synchrotron X-ray diffraction: a comparison with YNiO3

Rare-earth nickelates RNiO3 (R= Y, La…Lu) are electron-correlated perovskite materials where the interplay between charge and spin order results in a rich phase diagram, evolving from antiferromagnetic insulators to paramagnetic...

Prediction of the space group of perovskite-like compounds of the composition AII2BIIIB′VO6

The prediction of new compounds of the composition AII2BIIIB′VO6 was carried out, the type of distortion of their perovskite-like lattice, the space group were predicted, and the parameters of the crystal lattice of the predicted compounds were estimated. When predicting, only the property values of the chemical elements were used. Programs based on machine learning algorithms for various variants of neural networks, a linear machine, the formation of logical regularities, k-nearest neighbors, support vector machine showed the best results when predicting the type of distortion of a perovskite-like lattice. When evaluating the lattice parameters, the programs based on algorithms for orthogonal matching pursuit and automatic relevance determination regression were the most accurate methods. The accuracy of predictions of the perovskite-like lattice distortion type was no less than 74 %. The accuracy of estimating the lattice linear parameters was within ± 0.0120 – 0.8264 Å, and the accuracy for angles β with monoclinic distortion of the lattice was ± 0.08 – 0.74 deg. The calculations were carried out using systems based on machine learning methods. To evaluate the prediction accuracy, an exam recognition in the cross-validation mode was used for the compounds included in the sample for machine learning. The predicted compounds are promising for the search for new magnetic, thermoelectric and dielectric materials.

Magnetic Susceptibility and EPR Study of Bi₅Nb₃−₃ₓCo₃ₓO₁₅−δ

Magnetic susceptibility, microstructure and EPR of cobalt-containing solid solutions with layered perovskite-like structure Bi5Nb3−3xCo3xO15−δ have been studied. Solid solutions of Bi5Nb3−3xCo3xO15−δ (x60.005) can be crystallized in tetragonal syngony (sp. gr. P4/mmm), as cobalt content increases, monoclinic distortion of the unit cell emerges at 0.005 < x 6 0.04 (sp. gr. P2/m). The formation of exchange-bound aggregates of Сo(III) and Co(II) atoms predominantly with antiferromagnetic exchange types has been found in the solid solutions. EPR indirectly confirms that cobalt ions are in octahedral positions of substitution of Nb(V) ions