In-situ neutron diffraction of LaCoO3 perovskite under uniaxial compression. I. Crystal structure analysis and texture development

Abstract

The dynamics of texture formation, changes in crystal structure, and stress accommodation mechanisms have been studied in perovskite-type R3¯c rhombohedral LaCoO3 during uniaxial compression using in-situ neutron diffraction. The in-situ neutron diffraction revealed the complex crystallographic changes causing the texture formation and significant straining along certain crystallographic directions during compression, which are responsible for the appearance of hysteresis and non-linear ferroelastic deformation in the LaCoO3 perovskite. The irreversible strain after the first loading was connected with the appearance of non-recoverable changes in the intensity ratio of certain crystallographic peaks, causing non-reversible texture formation. However, in the second loading/unloading cycle, the hysteresis loop was closed and no further irrecoverable strain appeared after deformation. The significant texture formation is responsible for an increase in the Young's modulus of LaCoO3 at high compressive stresses, ranging from 76 GPa at the very beginning of the loading to 194 GPa at 900 MPa at the beginning of the unloading curve.

Stress-induced charge-ordering process in LiMn2O4

“…In the longitudinal direction under the compression, along the a-and c-axes the lattice exhibits a response of compressive strain; however, a tensile strain is observed along the b-axis even from the beginning (Figure 3), contradicting the normal elastic behaviors in the metal or ceramic materials. [21,28] Similar abnormal trends of the lattice strains are also observed in the transverse direction ( Figure S3), without showing a normal Poison's effect. Therefore, in addition to the elastic strain, it is a strain generated from the orthorhombic lattice distortion from the cubic at the phase transition, denoted as ε PT , that significantly contributes to the measured lattice strains at loading (Figures 3 and S3), resulting in the abnormal stress lattice strain behavior.…”

“…[18] In this paper, we report that the charge-ordering process can be induced and resolved as a function of continuously applied stress using in situ neutron diffraction. [19][20][21] The evolving process is followed by monitoring the lattice distortion solely contributed by the Jahn-Teller effects through eliminating the stress-induced elastic components. Specifically, the Jahn-Teller effects at the Mn(1), Mn (2) [10,12] and therefore, the monitored lattice strain evolution along those axes directly reflect the occurrence of Jahn-Teller distortion, or e g electron localization, at the particular Mn site.…”

In-situ neutron diffraction of LaCoO3 perovskite under uniaxial compression. II. Elastic properties

“…5,7,8 The properties of the LaCoO 3 ceramics are listed Table I. Most of the calculations performed in the current paper were done utilizing the neutron diffraction results obtained from Ref.…”

“…Most of the calculations performed in the current paper were done utilizing the neutron diffraction results obtained from Ref. 7. The present evaluation used the loading data during the neutron diffraction.…”

“…5,6 The results reported showed that the Young's modulus, measured from the slope of a stress-strain deformation curve, was equal to 76 GPa at the very beginning of uniaxial compression, but increased by almost 2.5 times to 194 GPa when measured at the beginning of unloading from a compressive stress of 900 MPa. 7 The texture and formation of preferred domain orientation during uniaxial compression were studied and it was shown that at high applied stress, there was a significant growth of ferroelastic domains with preferred crystallographic orientations at the expense of other domain orientations. Upon unloading in the first cycle, partial recovery/reappearance of other crystallographic domains was observed.…”