Hydrothermal synthesis and influence of later heat treatment on the structural evolution, optical and electrical properties of nanostructuredα-MoO₃single crystals

Abstract

In the current study, α-MoO3 nanocrystals were successfully synthesized from ammonium heptamolybdate tetrahydrate using a simple hydrothermal route. The influence of calcination temperature on the structural, optical and electrical properties was systematically investigated for the MoO3 powder products. The XRD results were analyzed for these powders, revealing the formation of a mixed phase (β- and α-MoO3) at calcination temperatures ranging from 350 °C–450 °C, and hence a residual monoclinic phase still exists in the samples at the calcination temperature of 450 °C. Subsequently, the mixed phase was completely converted to a pure single phase of α-MoO3 at a calcination temperature of 500 °C. The optical properties of the MoO3 powders were investigated using the transformed diffuse reflectance technique according to Kubelka–Munk theory. For such a powder product, the results of the optical measurements demonstrated the realization of indirect and direct allowed transitions at the spectral ranges 3.31–3.91 eV and 3.66–4.27 eV, respectively. The indirect- and direct-allowed band-gaps of the MoO3 products were found to increase from 2.69–3.12 eV and from 3.43–3.64 eV, respectively, by increasing the calcination temperature from 350 °C–600 °C. The MoO3 powders calcined at different temperatures were converted into five dense tablets for performing the electrical measurements. These measurements were carried out at different working temperatures using a system operating under high vacuum conditions. The results revealed that the dc-conductivity of such a tablet typically increases by more than five orders of magnitude with an increase in the working temperature from 77–300 K. These results also demonstrated a high dependence of dc-conductivity on the calcination temperature for the MoO3 products. The dc-conductivity as a function of the operating temperature revealed the presence of at least three different electrical conduction mechanisms for the same MoO3 tablet.

Hydrothermal Synthesis and Gas Sensing of Monoclinic MoO3 Nanosheets

“…Although the synthesis of the m-MoO 3 phase has been carried out by many methods (spray pyrolysis, pulsed laser thin-layer deposition, molecular beam epitaxy, o-MoO 3 conversion, solution-phase reaction, etc. ), it has not been prepared hydrothermally yet in pure form, only as a part of a mixture of MoO 3 polymorphs [18]. On the other hand, it would be useful because the hydrothermal method is simple, does not use high temperatures (usually it operates only between 100 and 250 • C), results in highly crystalline, monodisperse products, and metastable phases can be also synthetized by it.…”

Crystal Structure Refinement, Magnetic and Mössbauer Analysis of LaFeO3 Perovskite Synthesized by SOL-GEL method

“…Where, D is the crystallite size, 𝜃 is the Bragg angle, 𝜆 is the wavelength of the X-ray radiation; 𝛽 is the full width at half maximum height (FWHM) of the diffraction peak located at 2𝜃, the constant 𝑘 is taken as 0.9 [29].…”

The effect of gradient conductivity of doped BiFeO3 as filler on the surface insulation performance of epoxy composite

“…The plots (αE) 2 vs. E for P-BFO, BC5FO, BS5FO samples are shown in figure 4 according to Tauc relation. The indirect bandgap values for BFO ceramic samples were determined from the square of the Kubelka-Munk function versus energy and extrapolation of the linear part of F 2 (R) to zero value [25]. It was found that the bandgap values for BC5FO, P-BFO, BS5FO are 2.1819 eV, 2.2011 eV, 2.2170 eV, respectively.…”