Nanoindentation study of nickel manganite ceramics obtained by a complex polymerization method

The chemical synthesis of nickel manganite powder was performed by a  complex polymerization method (CPM). The obtained fine nanoscaled powders were uniaxially pressed and sintered at different temperatures: 1000–1200 °C for 2 h, and different atmospheres: air and oxygen. The highest density was obtained for the sample sintered at 1200 °C in an oxygen atmosphere. The energy for direct bandgap transition (Eg) calculated from the Tauc plot decreases from 1.51 to 1.40 eV with the increase of the sintering temperature. Indentation experiments were carried out using a three-sided 
pyramidal (Berkovich) diamond tip and Young's modulus of elasticity and hardness of NTC 
(negative temperature coefficient) ceramics at various indentation depths were calculated. The highest hardness (0.754 GPa) and elastic modulus  (16.888 GPa)  are exhibited by the ceramics sintered at  highest temperature in an oxygen atmosphere.