NDLI: A new type of antiferrodistortive structure in a double perovskite with Pb

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Blasco, Javier Lafuerza, Sara Subías, Gloria Cuartero, Vera García, Joaquín Stankiewicz, Jolanta Sánchez, Ma Concepción
Description	Author Affiliation: Blasco J ( Instituto de Ciencia de Materiales de Aragón, Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza., C/Pedro Cerbuna 12, 50009, Zaragoza, Spain. jbc@unizar.es)
Abstract	We have found a new structural transition in $Pb_{2}MnReO_{6}$ at 410 K. Above this temperature, $Pb_{2}MnReO_{6}$ is cubic with disordered and dynamic atomic displacements manifested in the large thermal parameters of Pb and O atoms. Below 410 K, the antiferrodistortive shift of 2/3 of $Pb^{2+}$ cations away from the high-symmetry cubic site produces a new type of monoclinic cell. The unit cell expands at the transition and the heat capacity shows a peak with thermal hysteresis. These features agree with a first order transition. The entropy content of the transition is quite low indicating that the structural disorder has not been completely removed in the low temperature phase. The monoclinic phase of $Pb_{2}MnReO_{6}$ shows thermally activated conductivity which does not vary when an external magnetic field is applied. A change in the slope of the resistivity curve, observed at the structural phase transition temperature, is related to a slight difference in the activation energy between both phases. It suggests that the condensation of the distortions likely affects the conduction mechanism. The isothermal magnetization measurements reveal the presence of ferromagnetic contributions below 85 K. The ac magnetic susceptibility shows a dynamic peak at 50 K and, in addition, zero-field-cooled and field-cooled magnetization curves diverge strongly below 80 K. These features might be signature of magnetic inhomogeneity. Magnetic loops, obtained at 5 K, do not show saturation in fields up to 9 T. Furthermore, the measured coercivity increases sharply at low temperature indicating an abrupt change in the magnetic anisotropy. We show that all these magnetic properties point out to a ferrimagnetic ordering of Mn and Re atoms in an intermediate valence state.
ISSN	14779226
Issue Number	13
Journal	Dalton Trans.
Volume Number	40
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2011-04-07
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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