Abstract
Ba2LnMoO6 double perovskites have been recently shown to display a wide range of interesting magnetic and structural properties; Ba2154SmMoO6 exhibits simultaneous antiferromagnetic order and a Jahn–Teller distortion. Here we report a high temperature neutron diffraction study of Ba2154SmMoO6 from 353 to 877K. The results evidence a tetragonal to cubic phase transition at 423K. Above this temperature the thermal displacement parameters of the oxygen atoms are modelled anisotropically as a result of a transverse vibration of the bridging oxygen. A smooth increase in the cell parameter a is observed with temperature for Ba2154SmMoO6.
Highlights
Perovskite related compounds are amongst the most widely studied because of their unique properties and versatile structure
Structural distortions can arise in perovskites in a number of ways; via ionic size effects leading to octahedral tilting [2,3] and through electronic phenomena such as the Jahn–Teller (JT) effect [4] and B site cation displacements [5]
In order to further investigate the crystal structure into the high temperature regime, a variable temperature neutron diffraction experiment has been performed on the molybdenum double perovskite Ba2154SmMoO6 between 353 and 877 K
Summary
Perovskite related compounds are amongst the most widely studied because of their unique properties and versatile structure. Orbitally degenerate Mo5þ s1⁄41/2 spins are geometrically frustrated as they are arranged on the corners of a lattice of edge sharing tetrahedra This frustration drives the formation of spin singlet dimers; a fraction of the spins remain unpaired and are observed in magnetic susceptibility data and mSR measurements [12]. In Ba2154SmMoO6, simultaneous antiferrromagnetic and orbital ordering were seen at 130 K; whereas in Ba2NdMoO6, orbital ordering occurred over a 70 K temperature range from 130 to 60 K—well above TN for this material so that there is a weaker correlation between orbital and magnetic ordering [9] In both materials, below the Jahn–Teller transition, the single Mo5þ electron occupies both the dxz and dyz orbitals resulting in an elongation of the apical Mo–O bond length [8,9]. In order to further investigate the crystal structure into the high temperature regime, a variable temperature neutron diffraction experiment has been performed on the molybdenum double perovskite Ba2154SmMoO6 between 353 and 877 K
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