الفهرس 
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Abstract
This thesis studied several topics in the manganite. We have studied the structural, electrical, magnetic properties and the thermoelectric power of a series of compounds (Nd0.6Sr0.4MnO3)1-x/(CrO3)x obtained by solid state reaction method and the effect of annealing temperature.
Rietveld refinement of XRD data reveals that all samples are single orthorhombic phase with a space group (Pnma).
There are three cases for CrO3 in NSMO3 matrix. The first one the CrO3 goes mainly to the perovskite structure Nd0.6Sr0.4MnO3 by react and replace Mn3+ with Cr3+ into it. The second one is the CrO3 goes in the grain boundaries. The third one is the CrO3 or Cr2O3 has occupied interstitial sites on the grain boundaries. It could be the presence of one or both per composite.
Temperature-dependent electrical resistivity (measured by van der pauw method) measurements have revealed metal to semiconducting transitions at certain temperature called transition temperature (Tms). Tms shifts to lower temperature as increase CrO3 content, for x ≤ 0.025 wt% exhibit transitions from semiconducting state to a metallic one on lowering temperature, beside for x≥ 0.030 wt% there is no metal-semiconductor transition.
The semiconducting region (T > Tms) there are two mechanisms have been proposed for the localized carriers. It was examined by two models (Small Polaron Hopping at (T > ӨD/2) and Variable Range Hopping model at (Tms < T < ӨD/2)) to understand the conduction mechanism of CMR materials