Structure evolution with Sr content of the perovskite‐like materials La2−xSrxCoTiO6 (0 ≤x≤ 0.5). (1st April 2014)

• Record Type: Journal Article
• Authors: Gómez‐Pérez, Alejandro; Pérez‐Flores, Juan Carlos; Ritter, Clemens; Boulahya, Khalid; Castro, German R.; García‐Alvarado, Flaviano; Amador, Ulises
• Is Part Of: Journal of applied crystallography. Volume 47:Part 2(2014:Apr.)
• Page Start: 745
• Page End: 754
• Publication Date: 2014-04-01
• Subjects: Crystallography -- Periodicals; 548.05
• DOI: 10.1107/S1600576714004907
• Languages: English
• ISSNs: 0021-8898

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <p>The oxide series La<sub>2−<italic>x</italic></sub>Sr<sub><italic>x</italic></sub>CoTiO<sub>6</sub> (0 ≤<italic>x</italic>≤ 1.0) belong to the perovskite family with general formula <italic>AB</italic>O<sub>3</sub>. The evolution of the room‐temperature structure as a function of the Sr content was studied using complementary techniques by applying the symmetry‐adapted modes formalism (<italic>AMPLIMODES</italic>). In the compositional range presented in this article (0 ≤<italic>x</italic>≤ 0.5), the compounds adopt distorted perovskite structures of monoclinic (space group <italic>P</italic>2<sub>1</sub>/<italic>n</italic>) or orthorhombic (space group <italic>Pnma</italic>) symmetry, both with octahedral tilting scheme (<italic>a</italic><sup>−</sup><italic>a</italic><sup>−</sup><italic>c</italic><sup>+</sup>) (out of phase along two perovskite main directions and in phase along the third direction). The main difference between these structures is the existence of rock‐salt order of <italic>B</italic> ions in the monoclinic symmetry, which is lost for <italic>x</italic>≥ 0.30. As the Sr content increases, a better matching of the <italic>A</italic>—O and <italic>B</italic>—O distances occurs. This is produced by an elongation of the <italic>A</italic>—O distance as La<sup>3+</sup> is replaced by the larger ion Sr<sup>2+</sup>, and the shortening of the <italic>B</italic>—O distance due to the oxidation of Co<sup>2+</sup> to Co<sup>3+</sup> induced by the aliovalent substitution. As a result, the cuboctahedral <italic>A</italic>‐site cavity becomes less and less distorted; the <italic>A</italic> ion tends to occupy its ideal positions, increasing its coordination and giving rise to a more symmetrical structure. In the whole compositional range, the symmetry‐adapted atomic displacements (modes) responsible for the out‐of‐phase tilting of the <italic>B</italic>O<sub>6</sub> octahedra remain active but those associated with the in‐phase tilting become negligible, anticipating for <italic>x</italic>≥ 0.6 a transition to a new structure with tilting scheme either (<italic>a</italic><sup>0</sup><italic>a</italic><sup>0</sup><italic>c</italic><sup>−</sup>) (space group <italic>I</italic>4/<italic>mcm</italic>) or (<italic>a</italic><sup>−</sup><italic>a</italic><sup>−</sup><italic>a</italic><sup>0</sup>) (space group <italic>Imma</italic>) or (<italic>a</italic><sup>−</sup><italic>a</italic><sup>−</sup><italic>a</italic><sup>−</sup>) (space group <italic>R</italic><inline-graphic xlink:href="ark:/27927/pgg55053hqn" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><italic>c</italic>).</p> </abstract>