A neutron diffraction study of the partial substitution of Ba with Sr in the layered cobaltites Y(Ba{1-x}Sr{x})Co{2}O{5:5}

AURELIO, G.; SÁNCHEZ, R. D.; CURIALE, J.; CUELLO, G. J.

Puerto Iguazú, Misiones, Argentina

Simposio; XIX LatinAmerican Symposium on Solid State Physics; 2008

Universidad del Litoral

Cobalt-oxide based materials have attracted considerable interest in the lastdecade because, as they belong to the family of strongly-correlated electronsystems, they were expected to exhibit similar properties to those in themanganites and cuprates. Among cobaltites, the layered compoundsemph{R}BaCo$_{2}$O$_{5+delta}$ (emph{R} being a rare earth) are currentlybeing intensively studied. Several factors strongly influence the physicalproperties of these cobaltites: the non--stoichiometry ($0 leq delta leq1$), the emph{R} cation size, the vacancies structural order, the cobalt spinstate order, and -- as we have shown in a recent work-- also the structuraldisorder introduced by doping the Ba site with small quantities of smallercations with the same valence state. As a part of our ongoing systematic studyof these layered cobaltites and, in particular, on the influence of structuraldisorder on their properties, we present in this work the results of a neutrondiffraction study of YBaCo$_2$O$_{5+delta}$ for $delta approx 0.5$,focussing on the effects of a partial substitution of Ba with Sr. Neutronthermodiffractograms were collected at the Institut Laue Langevin (ILL) inGrenoble, France for the compounds YBa$_{0.95}$Sr$_{0.05}$Co$_2$O$_{5.46}$($x_{ m{Sr}}=0.05$) and YBa$_{0.90}$Sr$_{0.10}$Co$_2$O$_{5.46}$($x_{ m{Sr}}=0.10$) in the temperature range 20~K~$leq T leq$~600~K. Wealso performed high resolution neutron diffraction experiments at selectedtemperatures for the samples $x_{ m{Sr}}=0.05$, $x_{ m{Sr}}=0.10$ and theparent compound $x_{ m{Sr}}=0$. All these measurements, refined using theRietveld method, allowed for a detailed study of the possible crystalstructures that arise in this system and its quantification, as well as of themagnetic arrangements of the cobalt ions at low temperatures, giving valuableinformation which is not accessible through other techniques. Our resultsindicate that, in contrast with the effect of substituting Ba sites with Ca,which destroys the AFM long-range order and stabilizes a ferrimagnetic,spin-state ordered phase, Sr seems to favor a tetragonal symmetry which ismore compatible with the AFM state observed in the parent compound. Moreover,the systematic study of substituted compounds helps to better understand thebehavior of the parent compound which had remained unclear for some time.