Formation of Nickel Oxide Nanocuboids in Ferromagnetic La2Ni1-xMn1+xO6

The control of the spontaneous formation of nanostructures at the surface of thin films is of strong interest in many different fields, from catalysts to microelectronics, because surface and interfacial properties may be substantially enhanced. Here, we analyze the formation of nickel oxide nanocuboids on top of La₂Ni_1−xMn_1+xO₆ double perovskite ferromagnetic thin films, epitaxially grown on SrTiO₃ (001) substrates by radio-frequency (RF) magnetron sputtering. We show that, by annealing the films at high temperature under high oxygen partial pressure, the spontaneous segregation of nanocuboids is enhanced. The evolution of the structural and magnetic properties of the films is studied as a function of the annealing treatments at different temperatures. It is shown that the formation of NiOx nanocuboids leads to a nanostructured film surface with regions of locally different electrical transport characteristics.

Polymorph exploration of bismuth stannate using first-principles phonon mode mapping

Accurately modelling polymorphism in crystalline solids remains a key challenge in computational chemistry. In this work, we apply a theoretically-rigorous phonon mode-mapping approach to understand the polymorphism in the ternary metal oxide Bi2Sn2O7. Starting from the high-temperature cubic pyrochlore aristotype, we systematically explore the structural potential-energy surface and recover the two known low-temperature phases alongside three new metastable phases, together with the transition pathways connecting them. This first-principles lattice-dynamics method is completely general and provides a practical means to identify and characterise the stable polymorphs and phase transitions in materials with complex crystal structures.

Rare earth double perovskites: a fertile soil in the field of perovskite oxides

This review summarizes the compositions, syntheses, and applications of rare earth A₂B′B′′O₆ double perovskites.

The effect of partial substitution of Ni by Mg on the structural, magnetic and spectroscopic properties of the double perovskite Sr2NiTeO6

In this report, the structural, magnetic and spectroscopic properties of the freeze-drying synthesized Sr2Ni1-xMgxTeO6 (x = 0.0, 0.1, 0.2, 0.3 and 0.5) oxides are analyzed by means of X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD), electron paramagnetic resonance, diffuse reflectance and magnetic susceptibility. The XRPD and NPD data analysis using the mode-crystallography approach have revealed that at room temperature (RT), all the compositions are monoclinically distorted with the space group I2/m. The high and low temperature analyses have shown that these materials suffer a series of three structural phase transitions. The EPR results have shown that the spectra of all the compositions are centred at g≈ 2.28, indicating a slightly distorted octahedral environment of Ni(2+), which is in agreement with the crystal structure analysis. The increase of the Mg(2+) content in Sr2Ni1-xMgxTeO6, provokes a decrease of the dipolar interaction effects and thus, the resonance becomes narrower. This resonance does not completely disappear which leads to the idea that the long-range magnetic order is not completely established when x≥ 0.3. The substitution of the Ni(2+) (S = 1) ions by Mg(2+) (S = 0) ions, also induces a weakening of the antiferromagnetic interactions, which is reflected in the diminishing of the absolute value of θ and the Néel temperature TN. The magnetic structure determination revealed the existence of an antiferromagnetic coupling for x- and z-spin components of the nickel atoms.

Structural phase transitions and photoluminescence properties of Eu3+ doped Ca(2−x)BaxLaNbO6 phosphors

Crystal structure evolution and luminescence properties of Eu³⁺ doped Ca_(2−x)Ba_xLaNbO₆ phosphors have been discussed depending on the Ca/Ba substitutions.

Structural phase transitions and magnetic and spectroscopic properties of the double perovskites Sr2Co1−xMgxTeO6 (x = 0.1, 0.2 and 0.5)

Structural and magnetic properties of a series of double perovskites are investigated by X-ray and Neutron diffraction, EPR and magnetic susceptibility. The structural and phase-transitions analysis are done using symmetry mode-analysis approach.