Disentangling octahedral distortion and symmetry breaking in the ordered double perovskite SrLaCoNbO 6
Year: 2026
Type: article
Abstract: We report a comprehensive high temperature structural investigation of the B-site ordered double perovskite SrLaCoNbO$_6$ using combined Raman spectroscopy and x-ray diffraction (XRD) over the range 25--900~$^\circ$C. Two distinct temperature-driven anomalies are identified at $T_\mathrm{OD} = 300\pm 25~^\circ$C and $T_\mathrm{PT} = 750\pm 25~^\circ$C through pronounced renormalizations in the phonon frequency and linewidth, accompanied by the evolution and suppression of characteristic XRD reflections. The low-temperature anomaly at $T_\mathrm{OD}$ is associated with an isostructural octahedral distortion within the monoclinic $P2_1/n$ phase. At $T_\mathrm{OD}$, the radial and angular distortion parameters of the CoO$_6$ and NbO$_6$ octahedra decrease to near-zero values before reversing upon further heating due to an inversion of the in-plane Co--O and Nb--O bond-length hierarchy. The high-temperature anomaly at $T_\mathrm{PT}$ corresponds to a symmetry-breaking structural phase transition from $P2_1/n$ to the monoclinic $I2/m$ phase, confirmed by group-theoretical analysis and Rietveld refinement. These results demonstrate that integrating temperature-dependent Raman spectroscopy with laboratory-based XRD, complemented by quantitative octahedral distortion analysis, provides a robust approach to disentangle isostructural octahedral distortions from symmetry-breaking phase transitions in complex double perovskite oxides without recourse to synchrotron or neutron diffraction facilities.
DOI: 10.1103/54pd-ry7l
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
Funders: U.S. Department of Energy, Iowa State University, Department of Science and Technology, Ministry of Science and Technology, India, University of New South Wales, Indian Institute of Technology Delhi, Office of Science, Australian Research Council, Science and Engineering Research Board, Basic Energy Sciences, Ames Laboratory
OpenAlex ID: W7221882793