STRUCTURAL PHASE-TRANSITIONS IN LA(2-X-Y)RE(Y)SR(X)CUO(4)

We present a powder neutron diffraction study of the structural phase transitions in La1.7-xSrxNd0.3CuO4 for x = 0.0 - 0.20. The tilting ang le of the CuO6 octahedra increases from T-HT with decreasing temperatu re. Below 100 K it is nearly temperature independent without any signi ficant change even at T-LT Due to the decrease of T-HT the tilting ang le decreases with the Sr content. The tilting axis changes from < 0,1, 0 > towards < 1,1,0 > at the LT-transition, For the LTO phase a linear relationship is found between the orthorhombic splitting and the squa re of the tilting angle.