Nanocrystalline composites based on CdCO3 and Mn3O4: Synthesis and properties

Highlights: • Pure & S²⁻ doped (Mn₃O₄)_x(CdCO₃)_1-x nanocomposites prepared& characterized. • Preparation method adopted is simple, economical & scalable. • Prepared(for the first time) nanocomposites exhibit useful physical properties. • S²⁻ doped CdCO₃nanocrystals expected to be useful in sunscreen devices. • Cole-Cole plots reveal 2 nanocomposites with higher conductivity. With the aim of discovering new useful materials we have attempted to synthesize pure and sulfur (2.5 and 5.0 wt%) doped (Mn₃O₄)_x(CdCO₃)_1-x nanocomposites (x = 0.0, 0.25, 0.5, 0.75 and 1.0) by a simple microwave assisted solvothermal method using a domestic microwave oven with the easily available chemicals. The structural and chemical characterizations were done by carrying out powder X-ray diffraction (PXRD), and energy dispersive X-ray spectroscopic (EDX) measurements. Scanning electron microscopic analysis (SEM) was carried out to study the morphology of the nanocrystals. The average crystallite sizes were estimated using the Scherrer formula and found to vary from 6.37 to 28.95 nm. The prepared samples were optically characterized by carrying out UV–Vis spectral measurements. The optical bandgap energies are found to vary within 2.4–2.9 eV for all the nanocrystals prepared except for the end members. The results of optical absorption measurements on pure and S²⁻ added CdCO₃ nanocrystals indicate that they are expected to be useful in sunscreen devices. From the thermogravimetric (TGA) and differential thermal (DTA) analyses the decomposition temperatures of the samples were found. From the electron paramagnetic resonance (EPR) analysis the g-factor values were determined and it varies from 2.1493 to 1.9995 for the nanocomposites. All the samples prepared were pelletized and subjected to DC and AC electrical measurements in order to characterize them electrically. The DC electrical conductivity increases with the increase in temperature (40–150 °C). The dielectric parameters, viz. dielectric constant (ε_r), dielectric loss factor (tan δ) and AC electrical conductivity (σ_ac) increase with the increase in temperature. From the impedance spectra we can notice a semicircle in the high frequency region indicating the ionic conduction which is more dominant at higher temperatures.