Papers by Keyword: Tetragonal

Abstract: In this research, SnO₂ nanostructure thin films were fabricated by spray pyrolysis method, using concentration of tin (Sn) salt solution deposited on a glass substrate at temperature of 450 °C. The tin solution was prepared by solves 2.2563gm of SnCl₂.2H₂O (molecular weight 219.4954 g/mole) in 100 ml of ethanol, then add 60 drops of pure hydrochloric acid ( HCl) using drop by drop technique. Different concentrations of antimony oxide (1%, 2%, 3%, 4%) hve been used to depose the thin films. The structure has been examined by X-ray diffraction technique, which shown that all films are polycrystalline with tetragonal rutile crystalline structure with preferential orientation in the (200) direction and, grain size decreases with increasing doping concentration. Optical measurements shown that the films are transparently in the visible region, with an average transmittance more then 80% and, sharp absorption edge nearly at 350 nm, the nature of the optical transition were direct allowed with band gap varies between (2.97 - 3.75 eV) which is directly proportional to doping concentration. The results also show that the doping has led to improved the response time of the sensing. Two kinds of gases NO₂ and NH₃ have been used to test the sensing performance, at different operating temperatures (R.T, 100, 200, 250, 300 and 350) oC , and bias voltage (3 Volt). For NO₂ gas the highest sensitivity was 77%, the shortest response time 2.9 s and the recovery time 19 s, while for NH₃ gas sensitivity was 11.5%, the response time 4.1 s and the shortest recovery time 20s,

Abstract: The objective of this research was to prepare multi–phase bismuth vanadate (BiVO₄) powder using the solvothermal method to be used as a photocatalyst. In the preparation step, bismuth nitrate and ammonium vanadate were used as the precursors with a mole ratio of 1:1. The mixed solution was diluted to 0.025 M with acetic acid and heated at 200 °C for 2 h in a Teflon–lined stainless steel autoclave vessel. Multi–phase BiVO₄ was obtained without calcination step. Multi–phase BiVO₄ was characterized by X–ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT–IR), and energy dispersive spectroscopy (EDS). The efficiency of multi–phase BiVO₄ for photocatalytic degradation of the mixed dye of methylene blue (MB) and rhodamine B (RhB) solution under UV light irradiation was studied. The concentration of the mixed dye solution was measured by UV–Vis spectrophotometry (UV–Vis). The effect of concentration of catalyst and pH of solution was studied. The optimum conditions for photocatalytic degradation of mixed dye solution were obtained at 0.8 g/L for concentration of multi–phase BiVO₄ and 7.78 for initial pH of the mixed dye solution.

Abstract: Graphene oxide (GO) powder was synthesized by modified Hummer’s method. Bismuth vanadate (BiVO₄) nanoparticle was synthesized by solvothermal method at 100 and 200°C for 3h. Composite graphene oxide and bismuth vanadate (GO/BiVO₄) nanoparticle were synthesized by mixed oxide method in weight ratio of 0.20:1.00. The physical and chemical properties were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS) and surface area analyzer (BET). The photocatalytic degradation of methomyl performance was determined by high performance liquid chromatograph (HPLC). Composite GO/BiVO₄ nanoparticle at 200°C for 3h was the highest photocatalytic degradation of methomyl.

Abstract: The high temperature phase transition of zirconia produced from commercial zirconyl chloride chemical was compared with that produced from a Malaysian zircon mineral. Zirconyl chloride was produced from zircon by using the hydrothermal fusion method. Initial XRD diffractogram of these samples at room temperature show that they are of amorphous structure. High temperature XRD studies was then performed on these samples; heated up to 1500°C. The XRD diffractograms shows that the crystalline structure of tetragonal zirconia was first observed and the monoclinic zirconia becomes more visible at higher heating temperature.

Abstract: Bismuth vanadate (BiVO₄) powder was synthesized by a modified microwave method. Bismuth nitrate pentahydrate, ammonium metavanadate and 2-propanol were used as the starting precursors. The final pH of solution was adjusted to 7 and irradiation power at 600 Watt for 2 and 6 min. The yellow powder was filtered and dried at 100 °C for 24h. The phase of BiVO₄ powder was characterized by X-ray diffractometer (XRD). Multi-phase of monoclinic and tetragonal phase was obtained without calcination step. The morphology of BiVO₄ powder was investigated by scanning electron microscope (SEM). The BiVO₄ powder was irregular in shape and agglomerated with the range particle of 0.1–0.3 μm. The functional group of BiVO₄ powder was investigated by fourier transform infrared spectrometer (FTIR). The wavenumber at 498–502 cm^-1 and 746–762 cm^-1 was corresponding to the vibration of Bi-O bending and VO₄^3- stretching, respectively.

Abstract: Bismuth vanadate (BiVO₄) powder was synthesized via the solvothermal method at 100200 °C for 26h by using acetic acid as solvent without calcination steps. The phase transition of BiVO₄ powder was studied by Xray diffraction (XRD). The morphology and chemical composition of BiVO₄ powder were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The functional groups of BiVO₄ powder was identified by Fourier transform infrared spectroscopy (FTIR).

Abstract: The highest piezoelectric and ferroelectric properties of lead zirconate titanate (PZT) occur in vicinity of morphotropic phase boundary (MPB). In MPB, crystalline phase ratios play a crucial role in determining the dielectric properties. In this paper, PZT nanoparticles were synthesized by a modified sol gel procedure and the effects of different solvents of methanol, ethanol, 1-propanol, and acetic acid on tetragonal, rhombohedral, and monoclinic phase ratios near the Pb (Zr_0.53Ti_0.47)O₃ were investigated. The X-ray diffraction results show the formation of almost pure perovskite structure in all samples. The volume fraction of tetragonal and rhombohedral phases, lattice constants, and lattice distortion were measured from the X-ray diffraction and Raman spectroscopic analysis for each solvent. Also, the domain size was compared between the solvents. A trace amount of monoclinic phase could be detected by Raman spectroscopy. The results show that acetic acid is the most appropriate solvent for synthesizing of PZT nanoparticles in which the tetragonal lattice parameters are c_t=4.16 Ǻ and a_t=4.02 Ǻ with a distortion of 3%. The tetragonal volume fraction is estimated about 77%. The particle size and degree of agglomeration were measured according to field emission electron microscopy and indicates that 70 nm particles were formed for acid-based sample.

Abstract: The effect of CeO₂ addition in zirconia toughened alumina (ZTA) was examined. The CeO₂ addition in weight percent (wt %) was varied from 0 wt% to 15 wt%. The fabricated samples were sintered at a temperature of 1600°C. The sintered samples were characterized their properties such as fracture toughness and phase determination. X-ray diffraction patterns confirm the constituent phases present in the samples were alumina and zirconia. Fracture toughness for each sample in the range of 5.878.38 MPam^1/2 respectively. It was observed that the addition of ceria increased the fracture toughness of the zirconia toughened alumina ceramic composites.

Abstract: Zirconia Toughened Alumina (ZTA) Nanocomposites were prepared using Nano sized Zirconia (ZrO2) powders doped with 3% mol of yttria (Y2O3) nanopowders. Diffusion of α-alumina (Al2O3) nanoparticles as well as yttria into the Zirconia lattice network drives monoclinic – tetragonal martensitic transformation. Zirconia toughened alumina (ZTA) composites containing different amount of partially stabilized Zirconia (PSZ) 5, 10, 15 and 20% mol, were prepared via wet mixing and axial pressing. After sintering at different temperatures,1450, 1550 and 1650 °C, phase change in the samples were monitored. X-ray diffraction patterns showed that at constant composition, tetragonal zirconia was increased by temperature increasing due to intensification of diffuse coefficient of alumina and yttria in the system. At constant temperature, remained monoclinic zirconia was increased with Zirconia content increasing.

Abstract: The anisotropy that is inherent to piezoelectricity is directly tied to the symmetry of domains within the crystals of polycrystalline piezoelectrics. Alloy design for these oxide materials is often focused on influencing pinning of domain walls in polycrystals that have been subjected to high fields and elevated temperatures to introduce the ‘poled’ condition from which most piezoelectric devices operate. We have investigated a wide range of these oxides consisting of single phases or mixtures of phases that may be all or partially piezoelectric in character. Crystal symmetries investigated include tetragonal, orthorhombic, rhombohedral and monoclinic with some phase transitions evolving during high-temperature processing or during poling. Materials investigated include a range of bismuth titanates, lead titanates, lead zirconate titanates and sodium niobates. A variety of texture evaluation techniques, including area detector x-ray diffraction, synchrotron x-ray sources, and neutron sources have been utilized along with Rietveld diffraction modeling tools to enable a deeper understanding of domain textures, domain texture evolution and synergistic relations between crystallographic textures and domain textures. This paper documents an understanding of texture and anisotropy in these materials, and provides insight on approaches to optimize textures for high performance in these materials and demonstrates how these tools can be used to evaluate processing variations from production of these materials.