Distinguish thermal transitions in different blocks in cuprates

Bi1.7Pb0.3Sr2Ca2Cu3O10+y was used as an example of Cuprates for our study. The subtle thermal transitions and the jumps of the parameters appear in the sample at about 300 and 700°C, respectively. The unit cell of the sample is composed of two structural blocks: perovskite and rock salt. The size of every block along c direction is about a nanometer. What should be made clear is whether the two thermal and structural changes take place in the whole cell or from different blocks. The bond lengths in the unit cell are analyzed carefully before and after two thermal and structural changes based on the results of X-ray diffraction. Careful analysis of the bond length in the samples demonstrates that the two jumps of the parameters are correlated with the two blocks. After the jump at about 300°C, the bond lengths in the rock salt block change more significant than in the perovskite block. After the jump at about 700°C, the bond lengths in the perovskite block change more significant than in the rock salt block. The change of the bond lengths clearly shows that the different thermal transitions and the jumps of the parameters take place in different blocks.