Nickel-lead-borate glasses and vitroceramics with antiferromagnetic NiO and nickel-orthoborate crystalline phases

We report a systematic investigation of structural, spectroscopic, optical and magnetic behavior of xNi(2)O(3)center dot(100 - x)[3B(2)O(3)center dot PbO2] vitroceramic system with x = 0-50 mol% Ni2O3 synthesized by melt quenching. X-ray diffraction investigation reveals the amorphous nature of samples with x <= 20 mol% Ni2O3 and the presence of NiO and Ni3B2O6 crystalline phases in samples with x >= 30 mol% Ni2O3. FTIR spectroscopy investigation demonstrates that increasing the Ni2O3 content of samples results in formation of B-O-Ni linkages, orthoborate and [NiO6] structural units. FTIR data show that acetylene can be adsorbed on the glassy surface, reacts with water from glass network resulting in acetaldehyde and acetic acid on samples surface. UV-Vis spectra of the nickel-lead-borate vitroceramic system show that nickel ions absorb light in the 250-1000 nm region. The value of optical band gap energy was found to vary between 4.21 and 4.34 eV. EPR data show that the increase of the Ni2O3 content in the 10 <= x <= 30 mol% Ni2O3 compositional range produces an enhancement of the resonance line from g similar to 2.21 assigned to the Ni+ 2 ions. This EPR resonance line was not observed for samples with x = 5 and 50 mol% Ni2O3. Magnetic susceptibility measurements indicate that for the x = 30 mol% Ni2O3 vitroceramic sample the effective magnetic moment per nickel ion becomes larger than that of samples with x < 30 mol% Ni2O3 suggesting a superparamagnetic behavior. This assumption is also supported by the magnetization versus magnetic field dependence. The superparamagnetic behavior of sample x = 30 mol% Ni2O3 is due to formation of NiO and Ni3B2O6 crystalline phases.