Structural properties, defects and structural phase transition in the   ROFeM (R=La, Nd; M=As, P) materials
  The structural properties of the ROFeM (R=La, Nd; M=As, P) materials have been analyzed by means of electron diffraction, high-resolution transmission-electron microscopy (TEM) and in-situ cooling TEM observations. The experimental results demonstrate that the layered ROFeM crystals often contain a variety of structural defects, such as stacking faults and small-angle boundaries. The in-situ TEM investigations reveal that, in association with the remarkable spin-density-wave (SDW) instability near 150 K, complex structural transitions can be clearly observed in both crystal symmetry and local microstructure features. 
C. Ma, L.J. Zeng, H.X. Yang, H.L Shi, R.C. Che, C.Y. Liang, Y.B. Qin,   G.F. Chen, Z.A. Ren, J.Q. Li