Insights into the structural symmetry of single-crystal YCrO$_3$ from synchrotron X-ray diffraction

Abstract

We report on the crystallographic information such as lattice parameters, atomic positions, bond lengths and angles, and local crystalline distortion size and mode of single-crystal YCrO 3 compound by a high-resolution synchrotron X-ray diffraction study. The data was collected at 120 K (below T N ∼ 141.5 K), 300 K (within [T N , T C ]), and 500 K (above T C ∼ 473 K). Taking advantages of high intensity and brilliance of synchrotron X-rays, we are able to refine collected patterns with the noncentrosymmetric monoclinic structural model (P12 1 1, No. 4) that was proposed previously but detailed structural parameters have not determined yet. Meanwhile, we calculated patterns with the centrosymmetric orthorhombic space group (Pmnb, No. 62) for a controlled study. Lattice constants a, b, and c as well as unit-cell volume almost increase linearly upon warming. We observed more dispersive distributions of bond length and angle and local distortion strength with the P12 1 1 space group. This indicates that (i) The local distortion mode of Cr2O 6 at 120 K correlates the formation of the canted antiferromagnetic order by Cr1-Cr2 spin interactions mainly through intermediate of O3 and O4 ions. (ii) The strain-balanced Cr1-O3(O4) and Cr2-O5(O5) bonds as well as the local distortion modes of Cr1O 6 and Cr2O 6 octohedra at 300 K may be a microscopic origin of the previously-reported dielectric anomaly. Our study demonstrates that local crystalline distortion is a key factor for the formation of ferroelectric order and provides a complete set of crystallography for a full understanding of the interesting magnetic and quasi-ferroelectric properties of YCrO 3 compound.

A comprehensive review on the ferroelectric orthochromates: Synthesis, property, and application

“…The observed weak ferroelectricity in permittivity was ascribed to local polarization field [250]. Zhao et al [168] tentatively demonstrated that the strain-balanced bonds of Cr1-O3(O4) and Cr2-O5(O5) and the local Cr1O 6 and Cr2O 6 octahedral distortion modes in P12 1 1 symmetry (see Fig. 34) could be the origin of the dielectric anomaly reported previously.…”

“…It is pointed out that the noncentrosymmetric monoclinic structure model (P12 1 1, No. 4) has not yet been confirmed experimentally, though Zhao et al [168] reported the corresponding crystallographic information of lattice parameters and atomic positions (see Table 5) of a YCrO 3 single crystal, taking advantages of the high-resolution synchrotron X-ray diffraction. The YCrO 3 compound presently possesses a centrosymmetric crystal structure that holds an inversion center, i.e., no net charge polar could be formed.…”

“…It is stressed that the magnetic structure model was reached based on in-house magnetization measurements with single crystals [209,228] and theoretical calculations [72,180]. Zhao et al [168] tentatively demonstrated that the local Cr2O 6 distortion modes give rise to the appearance of CAFM order by spin interactions of Cr1-Cr2 ions, mainly via the intermediate of O3 and O4 ions in the P12 1 1 space group (see Fig. 34).…”

“…Reproduced with permission from Ref. [168] Cr1(4b): (x, y, z) (0, 0, 0.75) (0, 0, 0.75) (0, 0, 0.75) (x, y, z) (0, 0, 0.5) (0, 0, 0.5) (0, 0, 0.5) Cr2(2a): (x, y, z) (0.5, 0, 0.75) (0.5, 0, 0.75) (0.…”

“…(c) Temperature dependence of Cr1-O1(O2)-Cr2, Cr1-O3(O4)-Cr2, and Cr1-O5(O6)-Cr2 bond angles. Figures(a-c) were reproduced with permission from Ref [168]…”