Structural and Magnetic Instabilities of La$_{2-x}$Sr$_x$CaCu$_2$O$_6$
  A neutron scattering study of nonsuperconducting La$_{2-x}$Sr$_x$CaCu$_2$O$_6$ (x=0 and 0.2), a bilayer copper oxide without CuO chains, has revealed an unexpected tetragonal-to-orthorhombic transition with a doping dependent transition temperature. The predominant structural modification below the transition is an in-plane shift of the apical oxygen. In the doped sample, the orthorhombic superstructure is strongly disordered, and a glassy state involving both magnetic and structural degrees of freedom develops at low temperature. The spin correlations are commensurate. 
C. Ulrich, S. Kondo, M. Reehuis, H. He, C. Bernhard, C. Niedermayer,   F. Bouree, P. Bourges, M. Ohl, H.M. Ronnow, H. Takagi...