Abstract
Structural, electrical and IR reflectivity have been investigated for hole doped Nd 2− x Ca x NiO 4+ δ . X-ray diffraction has shown that the orthorhombic strain decreases when x increases from 0.05 to 0.33; above the strain increases with x. The dc resistivity indicates a semi-conducting behaviour, which can be described using two conduction modes: a variable-range hopping (VRH) mode at low temperature and a thermically activated mode at high temperature. The temperature of change of conduction mode is function of doping rate. Besides, the thermal resistance of Nd 1.67Ca 0.33NiO 4 compound presents an incident around 200 K, which is attributed to a charge ordering. IR reflectivity does not show any difference in phonon region. But, it exhibits a Mott-Hubbard gap and a difference on plasma frequency depending on x.
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