Influence of dopant concentration on the structure and physical properties of Nd$_{1-x}$Pb$_{x}$MnO$_{3}$ single crystals

TL;DR

This study investigates how varying Pb dopant levels in NdMnO3 crystals influence their structural phase, symmetry, and transport properties, revealing a transition from tetragonal to cubic structure with increased doping.

Contribution

It provides detailed structural analysis of Nd$_{1-x}$Pb$_{x}$MnO$_{3}$ single crystals and links dopant concentration to phase transitions and property changes.

Findings

Structural phase change from tetragonal to cubic with increased Pb doping

Unit cell volume doubles in cubic phase compared to tetragonal

Transport transition temperatures T_c and T_MI increase with doping level

Abstract

The structure of Nd$_{1-x}$Pb$_{x}$MnO$_{3}$ 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 ($\it{P4/mmm}$) is comparable to that of parent NdMnO$_{3}$, the volume of cubic unit cell ($\it{Pm\bar{3}m}$) 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 $\it{T_{c}}$ and $\it{T_{MI}}$ increase with x.