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4 Acta Physica Polonica A

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Low Temperature Crystal Structure Behaviour of Complex Yttrium Aluminium Oxides YAlO_3 and Y_3Al_5O_{12}

100%

Senyshyn A. , Vasylechko L.

Acta Physica Polonica A

2013

tom 124

nr 2

329-335

Crystal structures of two yttrium aluminium oxides, namely YAlO_3 and Y_3Al_5O_{12}, were investigated in the temperature range 3.4-300 K by high-resolution neutron powder diffraction. Neither traces of phase transformations nor discontinuous changes of physical properties were observed. Thermal expansion of yttrium aluminium oxides was evaluated in terms of 1st order Grüneisen approximation, where the Debye temperatures and the Grüneisen parameters have been estimated for both compositions. Anomalies in the thermal expansion of yttrium aluminium perovskite have been observed and modelled using the Einstein oscillator with negative Grüneisen parameter. Extended bond length analysis revealed significant thermally-driven modifications of the aluminium-oxygen framework.

Synthesis and Structure Characterisation of Micro-and Nanocrystalline Powders of Dy_{1-x}R_xFeO₃ (R = La, Pr, Nd, Sm, Gd)

61%

Pavlovska O. , Lutsyuk I. , Kondyr A. , Zhydachevskyy Y. , Vakhula Y. , Pieniążek A. , Vasylechko L.

Acta Physica Polonica A

2018

tom 133

nr 4

802-805

This work deals with the study of the phase and crystal structure behaviour of new micro- and nanocrystalline ferrites Dy_{1-x}R_xFeO₃ obtained by solid state reactions (R = La, Pr) and sol-gel citrate (R = Nd, Sm, Gd) techniques. It was established that all synthesized samples adopt orthorhombic perovskite structure isotypic with GdFeO₃. Unit cell dimensions and atomic coordinates of the mixed rare earth ferrites derived by full profile Rietveld refinement technique agree well with the data of the "pure" DyFeO₃ and RFeO₃ compounds, thus proving formation of continuous solid solutions Dy_{1-x}R_xFeO₃ in the DyFeO₃-RFeO₃ systems (R = La, Pr, Nd, Sm, Gd). Peculiarity of the Dy_{1-x}La_xFeO₃ series is the lattice parameters crossover and formation of dimensionally tetragonal structure at x ≈0.97.

Thermal Behaviour of PrCo_{1-x}Fe_xO₃ Probed by X-ray Synchrotron Powder Diffraction and Impedance Spectroscopy Measurements

61%

Pekinchak O. , Sugak D. , Ubizskii S. , Suhak Y. , Fritze H. , Vasylechko L.

Acta Physica Polonica A

2018

tom 133

nr 4

798-801

Crystal structure and transport properties of the mixed praseodymium cobaltites-ferrites PrCo_{1-x}Fe_xO₃ have been studied in the temperature range of 298-1173 K by a combination of in situ X-ray synchrotron powder diffraction and temperature dependent impedance spectroscopy measurements. In situ high temperature powder diffraction examination of PrCo_{1-x}Fe_xO₃ series revealed considerable anomalies in the lattice expansion which are especially pronounced for the cobalt-rich specimens. These anomalies, which are reflected in a sigmoidal dependence of the unit cell dimensions and in the considerable increase of the thermal expansion coefficients, are obviously associated with transitions of Co^{3+} ions from low spin to the higher spin states and the coupled metal-insulator transitions, occurring in in rare earth cobaltites at the elevated temperatures. Indeed, the temperature-dependent impedance measurements clearly prove the change of conductivity type from dielectric to the metallic behaviour in the mixed cobaltite-ferrites PrCo_{1-x}Fe_xO₃ at the elevated temperatures.

Phase and Structural Behaviour of the PrAlO_{3}-SmAlO_{3} System

61%

Basyuk T. , Vasylechko L. , Fadeev S. , Berezovets V. , Trots D. , Niewa R.

Acta Physica Polonica A

2010

tom 117

nr 1

98-103

High resolution in situ X-ray powder diffraction applying synchrotron radiation and differential thermal analysis/scanning calorimetry methods have been used to examine the pseudo-binary system PrAlO_3-SmAlO_3. Two kinds of solid solutions with rhombohedral and orthorhombic structure exist at room temperature. At elevated temperatures, a continuous phase transition Pm3m ↔ R3c and a first-order transformation R3c ↔ Pbmn occur in the two respective phases. A sequence of low-temperature phase transformations R3c ↔ Imma ↔ C2/m has been detected in Pr_{1-x}Sm_xAlO_3 samples with x < 0.35. Based on in situ powder diffraction and differential thermal analysis/scanning calorimetry data, the phase diagram of the pseudo-binary system PrAlO_3-SmAlO_3 has been constructed.