Thermal characterization of synthesized y2O3-CeO2-ZrO2

Fine powders of CeO₂-stabilized tetragonal zirconia polycrystal (Ce-TZP) with and without Y₂O₃ dopants were fabricated through a coprecipitation process. The powder characteristics were evaluated by thermal differential analysis (DTA), thermogravimetric analysis (TGA), infrared spectra (IR) and X-ray diffraction. CeO₂ doping reduces the phase transformation temperature and significantly stabilizes the tetragonal phase. IR spectra imply that OH group is not closely related to the formation of metastable tetragonal phase. Size effect may, however, play a role in stabilizing the tetragonal phase. No appreciable distinction between undoped and Y₂O₃-doped Ce-TZP powders was observed in either DTA or TGA thermograms. The DTA thermogram for the alcohol-washed gel exhibits rather complicated exothermic peaks as compared to the as-synthesized coprecipitates. It is argued that this difference is attributed to the interaction between CeO₂ and ethyl alcohol during the fabrication process.     

X-ray and neutron diffraction studies of the incommensurate structural transition in β-ThBr4

As first shown by Raman scattering, tetragonal β-ThBr₄ undergoes a phase transition at 92 K, in which the fourfold axis is preserved. In fact, low temperature powder X-ray and neutron diffraction revealed very weak extra lines, which could not be indexed satisfactorily. On the other hand, neutron diffraction and inelastic scattering on single crystals can be interpreted as a tripling of the cell along the fourfold axis with an incommensurate modulation in this direction.     

Characterization of nano-crystalline ZrO2 synthesized via reactive plasma processing

Nano-crystalline ZrO₂ powder has been synthesized via reactive plasma processing. The synthesized ZrO₂ powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and FTIR spectroscopy. The synthesized powder consists of a mixture of tetragonal and monoclinic phases of zirconia. Average crystallite size calculated from the XRD pattern shows that particles with crystallite size 20 nm or less than 20 nm are in tetragonal phase, whereas particles greater than 20 nm are in the monoclinic phase. TEM results show that particles have spherical morphology with maximum percentage of particles distributed in a narrow size from about 15 nm to 30 nm.     

Sub-solidus phase equilibria in the NdF3-Nd2O3 system

The sub-solidus phase equilibria in the NdF₃-Nd₂O₃ system was investigated over the whole composition range by powder X-ray diffraction (XRD) and differential thermal analysis (DTA) between room temperature and 1573K. The intermediate compound neodymium oxyfluoride was found to exhibit tetragonal, rhombohedral and cubic modifications. The tetragonal phase exists over 20 to 40 m% Nd₂O₃ and rhombohedral phase has a fixed composition of 50 m% Nd₂O₃. The rhombohedral phase transforms to cubic at around 826K.     

Green hydrothermal synthesis and photoluminescence property of ZnO2 nanoparticles

ZnO₂ nanoparticles were synthesized via a green hydrothermal method using ZnO powder and 30% H₂O₂ aqueous solution as the starting materials, and characterized by X-ray diffraction (XRD), Raman spectra, energy dispersive X-ray (EDX) spectra, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and room temperature photoluminescence (RTPL) spectra. It was found that suitable reaction temperature (e.g., 80-140 °C) played an important role in obtaining pure cubic phase ZnO₂ nanoparticles. The RTPL spectra disclosed that the as-synthesized ZnO₂ nanoparticles exhibit one strong emission band centered at around 400 nm and one very weak emission band at around 474 nm, which may have originated from the band edge emission and the oxygen vacancy, respectively.     

Evidence of low-symmetry phases in pressure-dependent Raman spectroscopic study of BaTiO<Subscript>3</Subscript>

In the earlier pressure-dependent Raman spectroscopic studies, it has been reported that BaTiO₃ undergoes a tetragonal to cubic phase transition above ~ 2 GPa, whereas pressure-dependent X-ray absorption, X-ray diffuse scattering studies and pair distribution function studies have reported the presence of a low-symmetry rhombohedral phase above ~ 2.3 GPa. In this report, we present our pressure-dependent Raman spectroscopic studies on polycrystalline BaTiO₃ which shows that it first undergoes a transition from tetragonal to orthorhombic/rhombohedral phase above ~ 2.6 GPa and then finally goes to the cubic phase above 8.4 GPa. Pressure-dependent synchrotron X-ray diffraction (SXRD) studies have also been carried out that provided rate of change of volume as a function of pressure resulting in bulk modulus of 215 ± 9 GPa.     

Stabilization of the high-temperature phases of HfO2 by pulsed laser irradiation

Spherical hafnia nanoparticles have been prepared by laser ablation. The particle size has been shown to decrease with increasing incident laser intensity. X-ray diffraction and transmission electron microscopy data demonstrate that incident intensities above 5 × 10⁹ W/m² ensure the formation of the high-temperature (tetragonal and cubic) phases of hafnia. The nanoparticles obtained in this study exhibit good thermal stability.     

Study of structural and magnetoelectric properties of 1−x(Ba<Subscript>0.96</Subscript>Ca<Subscript>0.04</Subscript>TiO<Subscript>3</Subscript>)–x(ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>) ceramic composites

Multiferroic ceramic composites of (1?x)Ba_0.96Ca_0.04TiO₃–(x)ZnFe₂O₄ (BCT-ZF) were prepared from ferroelectric (FE) barium calcium titanate (BCT) and ferromagnetic (FM) zinc ferrite (ZF) by using the solid state reaction method with different mol% fractions of x (x?=?0.1 and 0.2). The preliminary structural studies carried out by X-ray diffraction at room temperature reveals that the samples have a tetragonal structure along with the cubic spinel ferrite phase. Raman spectra of the composites also confirm the existence of BCT phase and ZF phase. The room temperature ferroelectric polarization measurements as a function of magnetic field show the existence strong magnetoelectric coupling of 10.85 (mV/(cm.Oe).     

Spectroscopic and thermal behavior of ZnHg(SCN)4

The synthesis and purification of zinc mercury thiocyanate, ZnHg(SCN)₄ (ZMTC), are described. The identity of the synthesized compound was characterized by elemental analysis, X-ray powder diffraction, infrared, Raman, and UV/Vis/NIR transmission spectra. The thermal stability and thermal decomposition of ZMTC crystal were investigated by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements. The intermediates and final products of the thermal decomposition were identified by X-ray powder diffraction (XRPD).     

Nanocrystalline scheelite SrWO4: a low temperature co-fired ceramic optical material-synthesis and properties

Nanocrystalline strontium tungstate (SrWO₄) is synthesized through a single step modified combustion process. The X-ray diffraction, Fourier transform Raman and Infrared spectroscopy studies reveal that the as-prepared powder is single phase and possess tetragonal structure. The transmission electron microscopic investigations have shown that the particle size of the as prepared powder is in the range 18–22 nm. The optical constants are estimated from the UV–Visible studies and calculated optical band gap is 4.28 eV. The sample showed maximum transmission in the visible regions but poor transmittance in the ultraviolet region. The photoluminescence spectra recorded at different temperatures showed intense blue emission. The nanocrystalline SrWO₄ obtained by the present combustion method was sintered to 95 % density at a relatively lower temperature of 810 °C for 3 h. The dielectric constant (ε_r) and loss factor (tan δ) of the sintered SrWO₄ pellets at 5 MHz measured at room temperature were 9.9 and 6.29 × 10^?3 respectively. The experimental results obtained in this work demonstrate the application of SrWO₄ as UV filters, transparent films for window layers on solar cells, anti-reflection coatings, scintillators, detectors and for low-temperature co-fired ceramic applications.     

Controllable preparation of SnO2 nanoplates and nanoparticles via hydrothermal oxidation of SnS2 nanoplates

A facile hydrothermal oxidation route has been proposed for the controllable preparation of SnO₂ nanoplates and nanoparticles, using the home-made SnS₂ nanoplates as a precursor. It was found that the temperature played an important role in the microstructures of the obtained products. While nanoplates of tetragonal phase SnO₂ were synthesized via hydrothermal treatment of the SnS₂ nanoplates in 15 vol.% H₂O₂ aqueous solution at 180 °C for 24 h, only nanoparticles of tetragonal phase SnO₂ could be obtained via hydrothermal treatment of the SnS₂ nanoplates in 15 vol.% H₂O₂ aqueous solution at 200 °C for 24 h. The as-prepared products were characterized by means of X-ray diffraction, field emission scanning electron microscope, and Raman spectra, and their possible formation mechanisms were also discussed.     

Structure and microstructure of In4Te3 nanopowders prepared by solid state reaction

In this paper, we investigated the structure and microstructure of In₄Te₃ nanopowders obtained by mechanically alloying an In₇₅Te₂₅ powder mixture. Structural, chemical, thermal and vibrational studies of the In₇₅Te₂₅ powder mixture were carried out using X-ray diffraction, energy dispersive spectroscopy, transmission electron microscopy, differential scanning calorimetry and Raman spectroscopy. The orthorhombic In₄Te₃ phase (In₃Se₄-type) was nucleated in 2 h of synthesis, although non-reacted tetragonal indium (In) was still present at that time. Small amounts of cubic In₂O₃ phase were observed after 31 h of synthesis. Rietveld analyses allowed the measurement of mean crystallites sizes and phase fraction variations when milling times were increased. These analyses showed that, after 31 h of synthesis, about 65 wt% of In₄Te₃ phase contained mean crystallite sizes smaller than 27 nm and microstrains greater than 1.5%. The crystallite and interfacial components sizes were determined by high resolution transmission electron microscopy. Differential scanning calorimetry measurements showed the influence of nanometric crystallite sizes on the melting of the In₄Te₃ and non-reacted In phases. Raman measurements showed that the trigonal Te and α-TeO₂ modes, observed for the precursor Te powder, are absent for the sample milled for 31 h. The structural stability of the nanocrystalline phases of the In₇₅Te₂₅ sample milled for 31 h was attested by X-ray diffraction measurements performed twelve months after its production.     

Raman,FT-IR and dielectric studies of PZT 40/60 films deposited by MOD technology

Ferroelectric Pb(Zr_0.4Ti_0.6) O₃ (PZT 40/60) thin films with uniform composition have been fabricated using the metallo-organic precursor compounds lead di-ethylhexanoate Pb(C₇H₁₅COO)₂, titanium di-methoxy-di-neodecanoate Ti(OCH₃)₂(C₉H₁₉COO)₂ and zirconium octoate Zr(C₇H₁₅COO)₄. These metallo-organic precursors were stored for more than four years and are very stable in ambient conditions, compared to sol-gel solutions. The structural development of these films under different annealing temperatures was systematically studied using X-ray diffraction, FT-IR spectroscopy and Raman scattering. The results show that the overlapping of (h 0 0) and (0 0 I) peaks of the PZT 40/60 films in X-ray diffraction patterns, mainly due to the small grain sizes in films, makes it very difficult to distinguish individual diffraction peaks and to identify the phases. In FT-IR measurements, the intensity of Zr/TiO₆ metal-oxygen octahedral vibrational modes becomes stronger with increasing annealing temperatures, while the FT-IR spectral peaks of vibrations of the residual carbon ligands (COO^–) finally disappear at high temperatures, showing that FT-IR spectroscopy is a good way to monitor the growth of the perovskite phase in PZT 40/60 films. Raman measurements undoubtedly reveal the Raman spectra of these PZT 40/60 films in the tetragonal phase field, demonstrating that Raman spectroscopy is an effective tool to identify structures, especially in the case of thin films having small grains. The values of high dielectric constant and the total remanent polarization obtained by ferroelectric pulse measurements show that the PZT film is a suitable material for non-volatile random access memory and dynamic random access memory applications.     

Stress-induced shifting of the morphotropic phase boundary in sol-gel derived Pb(Zr0.5Ti0.5)O3 thin films

The structure evolution of Pb(Zr_0.5Ti_0.5)O₃ thin films with different thicknesses on the Pt(1 1 1)/Ti/SiO₂/Si substrates has been investigated using X-ray diffraction and Raman scattering. Differing from Pb(Zr_0.5Ti_0.5)O₃ bulk ceramic with a tetragonal phase, our results indicate that for PZT thin films with the same composition monoclinic phase with Cm space group coexisting with tetragonal phase can appear. It is suggested that tensile stress plays a role in shifting the morphotropic phase boundary to titanium-rich region in PZT thin films. The deteriorated ferroelectric properties of PZT thin films can be attributed mainly to the presence of thin non-ferroelectric layer and large tensile stress.     

Fabrication of BaTiO3 nanoparticles and its formation mechanism using the high temperature mixing method under hydrothermal conditions

Barium titanate (BaTiO₃) single-crystalline nanoparticles have been prepared via high temperature mixing method (HTMM) under hydrothermal conditions. The crystallized products were characterized by X-ray diffraction (XRD), filed emission scanning electron microscopy (FESEM), X-ray fluorescence (XRF), Raman spectra, transmission electron microscopy (TEM). The BaTiO₃ nanoparticles can be prepared at dilute KOH as compared with the method mixed at room temperature. The results show that the stoichiometric BaTiO₃ nanoparticles were synthesized at [Ba/Ti]_solution = 1. The high temperature will significantly narrow the solubility difference between the barium and titanium sources and leads to a burst nucleation from the solution. The defect mechanism is used to illustrate the time-dependent transformation from cubic to tetragonal phase.     

Temperature dependent growth and optical properties of SnO<Subscript>2</Subscript> nanowires and nanobelts

SnO₂ nanowires and nanobelts have been grown by the thermal evaporation of Sn powders. The growth of nanowires and nanobelts has been investigated at different temperatures (750–1000°C). The field emission scanning electron microscopic and transmission electron microscopic studies revealed the growth of nanowires and nano-belts at different growth temperatures. The growth mechanisms of the formation of the nanostructures have also been discussed. X-ray diffraction patterns showed that the nanowires and nanobelts are highly crystalline with tetragonal rutile phase. UV-visible absorption spectrum showed the bulk bandgap value (∼ 3–6 eV) of SnO₂. Photoluminescence spectra demonstrated a Stokes-shifted emission in the wavelength range 558–588 nm. The Raman and Fourier transform infrared spectra revealed the formation of stoichiometric SnO₂ at different growth temperatures.     

Structural Changes of YBa2Cu3O7-δSuperconductor with Co Substitution

YBa²(Cu^1-yCo^y)³O^7-δ superconductors with y = 0.00 ∼0.06 are synthesized. The content of oxygen increases with increase in cobalt content, while the oxidation of copper is almost independent of cobalt concentration. The orthorhombic-to-tetragonal transition occurs in the range of 0.028< y< 0.038 according to neutron powder diffraction studies on samples with y = 0.03. Structural refinements for X-ray and neutron diffraction data show that there is an orthorhombic phase with y≤0.02 and a tetragonal phase with y>0.04. There is an orthorhombic and a tetragonal phase coexisting in a sample withY = 0.03. The content of cobalt in the tetragonal phase (0.038) is larger than that in the orthorhombic one (0.028). It seems that the structure of YBa₂Cu_|1-y Co_{yO x} is unstable near the point of phase transition.     

Structural phase analysis,band gap tuning and fluorescence properties of Co doped TiO2 nanoparticles

This paper reports on structural and optical properties of Co (0, 3, 5 & 7 mol%) doped TiO₂ (titania) nanoparticles (NPs) synthesized by employing acid modified sol–gel method. The crystalline phase of the pure and doped NPs was observed with X-ray diffraction (XRD) followed by Raman scattering technique. Field emission scanning electron microscope and transmission electron microscopy give the morphological details. Fourier transform infrared spectra indicate the bonding interactions of Co ions with the titania lattice framework. Optical studies were attained with UV–visible absorption and fluorescence emission spectroscopy. XRD analysis reveals that all prepared samples have pure anatase phase with tetragonal symmetry devoid of any other secondary phase. The average crystallite size of all samples was calculated using Scherrer’s formula and was found to vary from 8 to 10 nm with doping concentration of Co. The Raman spectroscopy further confirmed the formation of TiO₂ in anatase structure in both pure and Co doped TiO₂ NPs. The most intense Raman active E_g peak of TiO₂ NPs shifted to higher energy on doping. Both UV–visible and fluorescence spectra show a blue shift in their absorption and band edge emission subsequently on increasing with Co percentage in titania host matrix, wherever there is an indication of quantum confinement effect with widening of band gap on decreasing in NPs size. There is also a possibility of strong Coulomb interaction effect on the optical processes involving the Co ions. However, the intensities of different emission spectra are not the same but decrease profoundly for doping samples due to concentration quenching effect.     

Red light from ZrO2:Eu nanostructures

Zirconia nanocrystals doped with europium ions were developed envisaging optical applications. The nanostructures were produced using zirconyl nitrate (ZrO(NO₃)₂·H₂O) and europium nitrate (Eu(NO₃)₃·5H₂O) as cation precursors, and urea (C₂H₅NO₂) as the fuel, by the combustion synthesis process. The lanthanide-doped nanostructures were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and photoluminescence. X-ray diffraction revealed the presence of tetragonal and monoclinic crystalline ZrO₂ phases. The latter was found to be a minority phase as identified by Raman and corroborated by the observed europium luminescence when compared to the intraionic emission in crystalline tetragonal fibres grown by the laser floating zone technique. Bright red europium luminescence is observed at room temperature when the combustion synthesized zirconia powders are excited with ultraviolet radiation. The spectroscopic properties of the europium ions in the powders are ascertained by comparing combined excitation–emission measurements with those from crystalline fibres.     

Effect of CuO additives on the reversibility of zirconia crystalline phase transitions

We have studied the influence of the differents atmospheres on the sintering of CuO-doped-zirconia ceramics. After an annealing treatment in a reducing atmosphere, we have found nanoparticles of metallic copper in triple points and in the grains of the sintered zirconia. Furthermore, the influence of the intergranular Y₂Cu₂O₅ phase on the tetragonal to monoclinic phase transition and the crystalline structure of zirconia is discussed with respect to results obtained from X-ray diffraction, differential thermal analysis, Raman spectroscopy and High Resolution Transmission Electron Microscopy.