Bulk Crystal Growth\nand Single-Crystal-to-Single-Crystal\nPhase Transitions in the Averievite CsClCu<sub>5</sub>V<sub>2</sub>O<sub>10</sub>

Quasi-two-dimensional averievites with triangle-Kagome-triangle\ntrilayers are of interest due to their rich structural and magnetic\ntransitions and strong spin frustration that are expected to host\na quantum spin liquid ground state with suitable substitution or doping.\nHerein, we report the growth of bulk single crystals of averievite\nCsClCu<sub>5</sub>V<sub>2</sub>O<sub>10</sub> with dimensions of several\nmillimeters on the edge in order to (1) address the open question\nof whether the room-temperature crystal structure is <i>P</i>3̅ m1, <i>P</i>3̅, or <i>P</i>2<sub>1</sub>/<i>c</i> or else, (2) to elucidate the nature of\nphase transitions, and (3) to study direction-dependent physical properties.\nSingle-crystal-to-single-crystal structural transitions at ∼305\nand ∼127 K were observed in the averievite CsClCu<sub>5</sub>V<sub>2</sub>O<sub>10</sub> single crystals. The nature of the transition\nat ∼305 K, which was reported as a <i>P</i>3̅\nm1-<i>P</i>2<sub>1</sub>/<i>c</i> transition,\nwas found to be a structural transition from high-temperature <i>P</i>3̅ m1 to low-temperature <i>P</i>3̅\nby combining variable-temperature synchrotron X-ray single crystal\nand high-resolution powder diffraction. In-plane and out-of-plane\nmagnetic susceptibility and heat capacity measurements confirm a first-order\ntransition at 305 K, a structural transition at 127 K, and an antiferromagnetic\ntransition at 24 K. These averievites are thus ideal model systems\nfor a deeper understanding of structural transitions and magnetism.