Rietveld Method The Cacu <sub> X </ Sub> Of Mn <sub> 3-x </ Sub> Mn <sub> 4 </ Sub> The O <sub> 12 </ Sub> Crystal Structure

Doped manganese oxides with the colossal magnetoresistance (CMR) is a strongly-correlated electron system.It has become a important research subject in the field of condensed matter physics and material science because of the important technological applications in magnetic recording, magnetic sensors, read heads for information storage and so on.From the perspective of application of the device, researchers have been committing to improving the low-field magnetoresistance and temperature stability of the magnetoresistance for manganese oxides materials. A great deal of attention has been attracted to CaCu₃Mn₄O₁₂manganites with perovskite-like structure not only for its large low field and well temperature stability but also for its special structure. It can modulate the micro-structures of materials and affect their physical properties by doping CaCu₃Mn₄O₁₂. In this article, the samples of CaCu_xMn_3-xMn₄O₁₂ (x=0.2, 0.4, 0.6, 0.7, 0.8 ) were synthesized by using the standard solid-state reaction technique. The micro-structure and structural phase transition of CaCu_xMn_3-xMn₄O₁₂ by the Rietveld refinements of powder X-ray diffraction patterns recorded at different temperatrue. The results showed that two phases (cubic with space group Im3 and trigonal with space group R3) coexist between 303K and 453K for CaCu_0.2Mn_6.8O₁₂. But there is only one trigonal phase with space group R3 between 303K and 393K for CaCu_0.4Mn_6.6O₁₂ .We think that there is a unknown phase except for the trigonal structrue( R3 ) for CaCu_0.4Mn_6.6O₁₂ when temperature is beyond 393K . The change of temprature leads to the structure distortion or even produces a new phase. The location of oxygen atoms, the bond angle and bond length change with the change of temprature, which indicates the presence of Jahn-Teller effect in MnO₆ octahedron. Lattice constant and unit cell volume change with the change of temprature.The background of powder X-ray diffraction patterns of CaCu_xMn_3-xMn₄O₁₂ (x=0.6, 0.7, 0.8) is relatively high, and the crystallographic quality of samples are not very good. It shows that these samples may have amorphous content. Therefore, solid-state reaction technique may not be suitable for preparation of CaCu_xMn_3-xMu₄O₁₂ with x lager than 0.6. Structural analysis is of great importance to further study the transport and magnetic properties of manganese oxides.