Structural Phase Transition in the 2D Spin Dimer Compound SrCu2(BO3)2
  A displacive, 2nd order structural phase transition at Ts=395 K from space group I`4 2 m below Ts to I 4/m c m above Ts has been discovered in the two-dimensional spin dimer compound SrCu2(BO3)2. The temperature evolution of the structure in both phases has been studied by X-ray diffraction and Raman scattering, supplemented by differential scanning calorimetry and SQUID magnetometry. The implications of this transition and of the observed phonon anomalies in Raman scattering for spin-phonon and interlayer coupling in this quantum spin system will be discussed. 
K. Sparta, G.J. Redhammer, P. Roussel, G. Heger, G. Roth, P. Lemmens,   A. Ionescu, M. Grove, G. Guentherodt, F. Huening, H....