Structural deformation of the S=1 kagome-lattice compound KV3Ge2O9

Abstract

The dielectric and structural properties of the $S=1$ kagome antiferromagnet ${\mathrm{KV}}_{3}{\mathrm{Ge}}_{2}{\mathrm{O}}_{9}$ are examined. The low-temperature structure below 50 K is orthorhombic with a typical correlation length of 8 nm. While the high-temperature hexagonal phase can be considered $C$-centered orthorhombic, the $C$-centered symmetry is broken below 50 K. The low-temperature symmetry does not support the simplex solid state, which is the theoretically expected ground state for the $S=1$ kagome lattice. Above 60 K, incommensurate lattice modulation is observed. The lock-in transition suggests that the origin of the orthorhombic deformation is the development of a short-range magnetic ordering.