Neutron Scattering - JUWEL - Forschungszentrum Jülich

HEiDi 13
Fig. 7 left: tetragonal HTT phase Fig. 7 right: orthorhombic´LTO phase
4.2 Twinning
During the transition into the low temperature phase the CuO6 octahedrons are tilted around
their [010] axis. Thus, the two axes of identical length in the HTT phase, a1 and a2, are not
equal in the LTO phase anymore. Instead, the longer one becomes the new a axis, the shorter
one becomes the b axis. Whether a1 or a2 becomes the new a axis depends only on the real
structure of the crystal, for instance grain boundaries or point defects. Therefore, one can find
two equivalent crystallographic space groups in the LTO phase:
Abma (a1 � a, a2 � b) and Bmab (a1 � b, a2 � a)
For the structure factors in the LTO is valid:
FAbma(hkl)=FBmab(khl)