Synthesis and characterization of the charge-transfer insulator KCuF$_{3}$

KCuF$_{3}$ is thought to be a prototypical orbital ordering material, with interesting properties that include a highly anistotropic superexchange ratio and one-dimensional spin dynamics down to a very low energy and temperature scale. High-quality single crystals of KCuF$_{3}$---with a typical size of roughly 3.6$\times $3.6$\times $2.5mm$^{3}$---were grown using an aqueous solution precipitation method. Room temperature x-ray powder diffraction measurements using Cu K$_{\alpha }$ radiation showed that the samples consisted of $>$90{\%} volume fractions of polytype a. Temperature-dependent Raman measurements provide evidence for structural instabilities between 50K and 300K in KCuF$_{3}$, including a decrease with decreasing temperatures (``softening'') of several phonon mode frequencies, and phonon mode splitting near 50K consistent with a tetragonal-to-orthorhombic (TO) transition that precedes the N\'{e}el transition at 40K. We argue that the TO structural transition is associated with rigid GdFeO$_{3}$-type rotations of the CuF$_{6}$ octahedra.