Influence of dopant concentration on the structure and physical properties of Nd₁₋ₓPbₓMnO₃ single crystals

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The structure of Nd₁₋ₓPbₓMnO₃ crystals is determined by single crystal X-ray diffraction. Substitution of Pb at the Nd site results in structural phase change from tetragonal (x = 0.25) to cubic (x = 0.37). These changes are attributed to the progressive removal of inter-octahedral tilting and minimization of the octahedral distortion leading to a higher symmetry as doping concentration increases. While the unit cell volume of tetragonal structure (P4/mmm) is comparable to that of parent NdMnO₃, the volume of cubic unit cell (Pm3m) is doubled. Electron diffraction patterns support these results and rule out the possibility of twinning. Changes in transport properties as a function of temperature at different doping levels are in accordance with the observed structural changes. It is noticed that Tc and TMI increase with x.