This article is cited in
5 papers
CONDENSED MATTER
Phase transitions in frustrated slightly nonstoichiometric ErBaCo$_4$O$_{7+x}$ ($x\approx0$, $0.03$) cobaltites
Z. A. Kazei,
V. V. Snegirev,
M. S. Stolyarenko Moscow State University, Moscow, 119992 Russia
Abstract:
The results of the first experimental studies on the structural (lattice parameters) and elastic characteristics of ErBaCo
$_4$O
$_{7+x}$ cobaltites in the range of structural and magnetic phase transitions are presented. The samples obtained using different thermal treatments and characterized by a small oxygen excess
$x$ are studied. It is found that the parameter
$\Delta a/a$ for the stoichiometric ErBaCo
$_4$O
$_7$ sample annealed in vacuum exhibits no anomalies in the course of a structural transition, whereas the parameters
$b$ and
$c$ undergo stepwise changes of opposite signs. The different values of these changes
$\Delta b/b\approx 4\times10^{-3}$ and
$\Delta c/c\approx-5\times10^{-3}$ result in the stepwise volume change
$\Delta V/V\approx -10^{-3}$. A slight deviation from the oxygen stoichiometry affects the character of the structural distortion; namely, the magnitude of the anisotropic strain and the sign of the isotropic strain change. The structural distortion in the stoichiometric sample is accompanied by a sharp stepwise change in the Young's modulus
$\Delta E(T)/E_0\sim 8\times10^{-2}$, whereas the magnitude of elastic anomalies near
$T_{\mathrm{S}}$ in slightly nonstoichiometric samples with
$x \sim 0.03$ decreases by an order of magnitude. Comparison of elastic anomalies manifesting themselves near the magnetic phase transition temperature
$T_{\mathrm{N}}$ for distorted samples with different deviations from stoichiometry suggests that the arising long-range magnetic order in the cobalt subsystem is apparently affected not only by structural distortions but also by disorder introduced by nonstoichiometric oxygen.
Received: 04.06.2020
Revised: 14.06.2020
Accepted: 17.06.2020
DOI:
10.31857/S1234567820150082
Fulltext:
PDF file (381 kB)