Effect of isovalent substitution of lanthanum atoms on the slab structure of ВаLa1- xNdxInO4 indates

1Titov, Yu.A
1Belyavina, NM
1Slobodyanik, MS
2Chumak, VV
Timosсhenko, MV
1Sliva, TYu.
1Taras Shevchenko National University of Kyiv
2Ivan Franko State University of Zhytomyr
Dopov. Nac. akad. nauk Ukr. 2020, 5:86-94
Section: Chemistry
Language: Ukrainian

The boundary of the isovalent substitution of a lanthanum atom by a neodymium atom in the slab perovskitelike structure of ВаLa1 – xNdxInO4 indates (0 ⩽ х ⩽ 0.25) has been determined using the X-ray powder diffraction methods. The crystal structure calculations were performed by use of the software package containing a full complex of the Rietveld procedures, including the crystal structure determination in multiphase samples. As a result, it was shown that, in fact, the ВаLa1 – xNdxInO4 (x = 0.2) synthesis product contains two polymorphic modifications of a slab perovskite-like structure, namely: the main orthorhombic ВаLa0,8Nd0,2InO4 phase with space group Pbca and the additional tetragonal one with space group I4/mmm. It was shown that the crystal structure of each ВаLa1 – xNdxInO4 modification is formed by the two-dimensional perovskite-like blocks constructed from a slab of distorted InO6 octahedra joined by their vertices. These blocks are separated by the slab of (Ba,La,Nd)О9 polyhedra. Here, the blocks are connected through —O—(Ва,La,Nd)—O— bonds, while there are no direct In—O—In bonds between the octahedra of adjacent blocks. Analysis of the structural features of the orthorhombic ВаLa0,8Nd0,2InO4 modification has shown that the isovalent substitution of lanthanum atoms by smaller-size neodymium atoms leads as to a significant (more than one and a half times) increase in the deformation degree of the interblock (Ba,La,Nd)O9 polyhedra, as well to a decrease in the (Ba,La,Nd)—О2 interblock length. Such structural changes result in a destabilization of the interblock “stitching” and become one of the main destruction factors of the slab perovskite-like structure of the ВаLa1 – xNdxInO4 phases at x > 0.25 and cause the absence of the BaNdInO4 indate

Keywords: compounds of An+1BnO3n+1 type, isomorphism, slab perovskite-like structure, X-ray powder diffraction

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