Synthesis and crystallization behavior of 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) nanosized powders prepared using a simple co-precipitation process

The synthesis and crystallization behavior of 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) nanopowders prepared using a simple co-precipitation process at 348 K and pH = 7 were investigated using differential scanning calorimetry/thermogravimetry (DSC/TG), an X-ray diffractometer (XRD), the Raman spectra, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and an energy dispersive spectrometer (EDS). The activation energy of tetragonal ZrO₂ crystallization from 3Y-TZP freeze-dried precursor powders using a non-isothermal method, namely, 169.2 ± 21.9 kJ mol⁻¹, was obtained. The growth morphology parameter n was approximated as 2.0, which indicated that it had a plate-like morphology. The XRD, Raman spectra, and SAED patterns showed that the phase of the tetragonal ZrO₂ was maintained at 1273 K. The crystallite size of 3Y-TZP freeze-dried precursor powders calcined at 1273 K for 5 min was 21.3 nm.     

Solvothermal synthesis of monodisperse ultrasmall cubic-structure Ba2YbF7 nanocrystals with intense upconversion

A series of monodisperse ultrasmall Ba₂YbF₇ nanocrystals with intense upconversion emission were synthesized via a facile solvothermal method by using oleic acid as capping ligands. X-ray diffraction (XRD) and transmission electron microscopy (TEM) assays revealed that the as-synthesized Ba₂YbF₇ nanocrystals are of cubic structure, rather than the reported tetragonal structure. The cell parameter of the particles is 5.918 Å. The Er³⁺ or Tm³⁺ doped Ba₂YbF₇ nanocrystals with the size of sub-10 nm can give an intense upconversion emission under the 980 nm laser excitation and the upconversion processes were discussed. The Ba₂YbF₇ nanocrystals show a potential application as a bioimaging agent.     

Electrophoretic enhanced micro arc oxidation of ZrO2-HAp-TiO2 nanostructured porous layers

Micro arc oxidation (MAO) and electrophoretic deposition (EPD) processes were simultaneously employed to grow ZrO₂-HAp-TiO₂ porous layers on titanium substrates under different conditions. Influence of the electrolyte composition and the growth time on surface morphology, topography, phase structure, and stoichiometry of the layers was investigated. The utilized electrolytes consisted of β-glycerophosphate, calcium acetate, sodium phosphate, and micron sized yttria-stabilized zirconia with different concentrations. AFM and SEM evaluations revealed a rough surface with a porous structure with a pores size of 50-750 nm. The pores size increased with the time and the electrolyte concentration. Based on the XRD and XPS results, the layers consisted of anatase, hydroxyapatite, monoclinic ZrO₂, tetragonal ZrO₂, ZrO, CaTiO₃, and α-TCP phases whose fractions were observed to change depending on the synthesis conditions. The average crystalline size of the HAp phase was determined as ∼54 nm. The nano-sized zirconia particles (d = 20-60 nm) were dispersed not only on surface, but also in depth of the layers. Utilizing thicker electrolytes and prolonging the growth time resulted in decomposition of hydroxyapatite as well as tetragonal ZrO₂ to monoclinic ZrO₂. EDX results also showed that the zirconium wt% in the layers increased with the time. EPD-enhanced MAO (EEMAO) technique was expressed as an efficient route to fabricate ZrO₂-HAp-TiO₂ multiphase systems within short times and only in one step.     

Growth and characterization of tetragonal structure modification of β-Gd2Si2O7:Ce

Growth procedure, crystal structure, and luminescent properties of tetragonal β-Gd₂Si₂O₇:0.5 at.% Ce (a = 6.65740(10) Å, c = 24.2715(3) Å, sp.gr. P4₃) are studied. Tetragonal modification of this compound is obtained for the first time. Essentially it is isostructural to β-Sm₂Si₂O₇ and some other known disilicates (Ca, La, Ce, Pr, Nd). Obtained samples demonstrate high luminescence yield under X-rays and fast decay.     

Synthesis of highly tetragonal BaTiO3 nanopowders by a two-step alkoxide-hydroxide route

BaTiO₃ (BT) nanopowders were synthesized using the alkoxide-hydroxide route. Formation of BT nanopowders commenced at 60 °C and their amount increased with increasing temperature. However, a TiO₂ second phase was always developed at temperatures higher than 100 °C due to the insufficient amount of H₂O caused by its evaporation. Therefore, a two-step process is presented herein for the synthesis of homogeneous, highly tetragonal BT nanopowders. The cubic BT nanopowders were synthesized at 100 °C and subsequently heated to high temperatures (>200 °C) to increase their tetragonality. Homogeneous BT nanopowders with an average size of 94.8 nm and a high c/a ratio of 1.0081 were obtained for the specimens synthesized at 260 °C for 60 h after the formation of the cubic BT nanopowders at 100 °C for 20 h.     

Morphology control and electrochemical properties of nanosize LiFePO4 cathode material synthesized by co-precipitation combined with in situ polymerization

Nanosize carbon coated LiFePO₄ cathode material was synthesized by in situ polymerization. The as-prepared LiFePO₄ cathode material was systematically characterized by X-ray diffraction, thermogravimetric-differential scanning calorimetry, X-ray photo-electron spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy techniques. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images revealed that the morphology of the LiFePO₄ consists of primary particles (40-50 nm) and agglomerated secondary particles (100-110 nm). Each particle is evenly coated with an amorphous carbon layer, which has a thickness around 3-5 nm. The electrochemical properties were examined by cyclic voltammetry and charge-discharge testing. The as-prepared LiFePO₄ can deliver an initial discharge capacity of 145 mAh/g, 150 mAh/g, and 134 mAh/g at 0.2 C, 1 C, and 2 C rates, respectively, and exhibits excellent cycling stability. At a higher C-rate (5 C) a slight capacity loss could be found. However after being charge-discharge at lower C-rates, LiFePO₄ can be regenerated and deliver the discharge capacity of 145 mAh/g at 0.2 C.     

Densification and mechanical properties of fine-grained Al2O3-ZrO2 composites consolidated by spark plasma sintering

Alumina matrix composites containing 5 and 10 wt% of ZrO₂ were sintered under 100 MPa pressure by spark plasma sintering process. Alumina powder with an average particle size of 600 nm and yttria-stabilized zirconia with 16 at% of Y₂O₃ and with a particle size of 40 nm were used as starting materials. The influence of ZrO₂ content and sintering temperature on microstructures and mechanical properties of the composites were investigated. All samples could be fully densified at a temperature lower than 1400 °C. The microstructure analysis indicated that the alumina grains had no significant growth (alumina size controlled in submicron level 0.66-0.79 μm), indicating that the zirconia particles provided a hindering effect on the grain growth of alumina. Vickers hardness and fracture toughness of composites increased with increasing ZrO₂ content, and the samples containing 10 wt% of ZrO₂ had the highest Vickers hardness of 18 GPa (5 kg load) and fracture toughness of 5.1 MPa m^1/2.     

CuIn1−xAlxS2 thin films prepared by sulfurization of metallic precursors

CuIn_1−xAl_xS₂ thin films (x = 0, 0.09, 0.27, 0.46, 0.64, 0.82 and 1) with thicknesses of approximately 1 μm were formed by the sulfurization of DC sputtered Cu-In-Al precursors. All samples were sulfurized in a graphite container for 90 min at 650 °C in a 150 kPa Ar + S atmosphere. Final films were studied via X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-Raman spectroscopy. It was found that all samples were polycrystalline in nature and their lattice parameters varied slightly nonlinearly from {a = 5.49 Å, c = 11.02 Å} for CuInS₂ to {a = 5.30 Å, c = 10.36 Å} for CuAlS₂. No unwanted phases such as Cu_2−xS or others were observed. Raman were recorded at a room temperature and the most intensive and dominant A₁ phonon frequency varied nonlinearly from 294 cm⁻¹ (CuInS₂) to 314 cm⁻¹ (CuAlS₂).     

Synthesis, structure, and high temperature Mössbauer and Raman spectroscopy studies of Ba1.6Sr1.4Fe2WO9 double perovskite

Ba_1.6Sr_1.4Fe₂WO₉ has been prepared in polycrystalline form by solid-state reaction method in air, and has been studied by X-ray powder diffraction method (XRPD), and high temperature Mössbauer and Raman spectroscopies. The crystal structure was resolved at room temperature by the Rietveld refinement method, and revealed that Ba_1.6Sr_1.4Fe₂WO₉ crystallizes in a tetragonal system, space group I4/m, with a = b = 5.6489(10)Å, c = 7.9833(2)Å and adopts a double perovskite-type A₃B′₂B″O₉ (A = Ba, Sr; B′ = Fe/W, and B″ = Fe/W) structure described by the crystallographic formula (Ba_1.07Sr_0.93)_4d(Fe_0.744W_0.256)_2a(Fe_0.585W_0.415)_2bO₆. The structure contains alternating [(Fe/W)_2aO₆] and [(Fe/W)_2bO₆] octahedra. Mössbauer studies reveal the presence of iron in the 3+ oxidation state. The high temperature Mössbauer measurements showed a magnetic to paramagnetic transition around 405 ± 10 K. The transition is gradual over the temperature interval. The decrease in isomer shift is in line with the general temperature dependence. While the isomer shift is rather linear over the whole temperature range, the quadratic dipolar ΔE temperature dependence shows an abrupt change at 405 K. The latter results allow concluding that a temperature-induced phase transition had occurred. The high temperature Raman study confirms the Mössbauer results on the magnetic to paramagnetic transition.     

Dielectric and microwave properties of ZrO2 doped CaO-SiO2-B2O3 ceramic matrix composites

The behavior of dielectric and microwave properties against sintering temperature has been carried out on CaO-SiO₂-B₂O₃ ceramic matrix composites with ZrO₂ addition. The results indicated that ZrO₂ addition was advantageous to improve the dielectric and microwave properties. X-ray diffraction (XRD) patterns show that the major crystalline β-CaSiO₃ and a little SiO₂ phase existed at the temperature ranging from 950 °C to 1050 °C. At 0.5 wt% ZrO₂, CaO-SiO₂-B₂O₃ ceramic matrix composites sintered at 1000 °C possess good dielectric properties: ?_r = 5.85, tan δ = 1.59 × 10⁻⁴ (1 MHz) and excellent microwave properties: ?_r = 5.52, Q · f = 28,487 GHz (11.11 GHz). The permittivity of Zr-doped CaO-SiO₂-B₂O₃ ceramic matrix composites exhibited very little temperature dependence, which was less than ±2% over the temperature range of −50 to 150 °C. Moreover, the ZrO₂-doped CaO-SiO₂-B₂O₃ ceramic matrix composites have low permittivity below 5.5 over a wide frequency range from 20 Hz to 1 MHz.     

Synthesis and characterization of spherical and rod like nanocrystalline Nd2O3 phosphors

Spherical and rod like nanocrystalline Nd₂O₃ phosphors have been prepared by solution combustion and hydrothermal methods respectively. The Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd₂O₃ has been obtained with calcination at 900 °C for 3 h and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of Nd₂O₃ phosphors show the formation of nanorods in hydrothermal synthesis whereas spherical particles in combustion method. TEM results also confirm the same. Raman studies show major peaks, which are assigned, to F_g and combination of A_g + E_g modes. The PL spectrum shows a series of emission bands at ∼326-373 nm (UV), 421-485 nm (blue), 529-542 nm (green) and 622 nm (red). The UV, blue, green and red emission in the PL spectrum indicates that Nd₂O₃ nanocrystals are promising for high performance materials and white light emitting diodes (LEDs).     

The effects of temperature and composition on the thermal conductivities of [(ZrO2)1−x(CeO2)x]0.92(Y2O3)0.08 (0 ? x ? 1) solid solutions

The thermal conductivities of [(ZrO₂)_1−x(CeO₂)_x]_0.92(Y₂O₃)_0.08 (0 ? x ? 1) solid solutions are studied in this paper. The incorporation of ZrO₂ and CeO₂ in the solid solution decreases the thermal conductivity compared with their end members (YSZ and YDC). The thermal conductivities of the solid solutions show clearly different temperature dependences in the ZrO₂-rich (0 ? x ? 0.5) region and in the CeO₂-rich region (0.5 ? x ? 1). The composition and the temperature dependence of the thermal conductivities are discussed based on established phonon scattering theories. We have concluded that the composition dependence of the thermal conductivity of this system is mainly controlled by the mass difference between Zr⁴⁺ and Ce⁴⁺, while the thermal conductivity-temperature relationship is dominated by the randomness of the defect distribution.     

Microwave dielectric properties of (1 − x)ZnMoO4-xTiO2 composite ceramics

(1 − x)ZnMoO₄-xTiO₂ (x = 0.0, 0.05, 0.158, 0.25, and 0.35) composite ceramics were synthesized by the conventional solid state reaction process. The sintering behavior, phase composition, chemical compatibility with silver, and microwave dielectric properties were investigated. All the specimens can be well densified below 950 °C. From the X-ray diffraction analysis, it indicates that the triclinic wolframite ZnMoO₄ phase coexists with the tetragonal rutile TiO₂ phase, and it is easy for silver to react with ZnMoO₄ to form Ag₂Zn₂(MoO₄)₃ phase and hard to react with TiO₂. When the volume fraction of TiO₂ (x value) increasing from 0 to 0.35, the microwave dielectric permittivity of the (1 − x)ZnMoO₄-xTiO₂ composite ceramics increases from 8.0 to 25.2, the Q_f value changes in the range of 32,300-43,300 GHz, and the temperature coefficient τ_f value varies from −128.9 to 157.4 ppm/°C. At x = 0.158, the mixture exhibits good microwave dielectric properties with a ?_r = 13.9, a Q_f = 40,400 GHz, and a τ_f = +2.0 ppm/°C.     

Growth, crystal structure and optical properties of layered dibarium cadmium diborate, Ba2Cd(BO3)2

A novel dibarium cadmium diborate, Ba₂Cd(BO₃)₂, has been successfully synthesized by standard solid-state reaction. Large sheet-like crystal with size up to 20 mm × 15 mm × 0.7 mm has been obtained using top-seed solution growth method. Ba₂Cd(BO₃)₂ crystallizes in the monoclinic space group C2/m with a = 9.6305(4) Å, b = 5.3626(3) Å, c = 6.5236(2) Å, β = 118.079(3)°, Z = 2. The crystal structure is composed of isolated [BO₃] triangles, [CdO₆] octahedra and [BaO₉] polyhedra. CdO₆ are vertex-connected with six BO₃ to form infinite _∞[Cd(BO₃)₂] layers extending in (0 0 1) plane, and two rows of Ba atoms closely occupy two side of _∞[Cd(BO₃)₂] layers to forming stoichiometric sheets. IR and transmittance spectrum of Ba₂Cd(BO₃)₂ were reported.     

Effect of Th doping on superconductivity in CePt3Si

Alloys from the solid solution Ce_1−xTh_xPt₃Si (x = 0.0, 0.02, 0.04, 0.08, 0.1, 0.2 and 1.0) were prepared by arc-melting. X-ray Rietveld powder analyses revealed that alloys in the compositional range 0 ≤ x ≤ 0.2 crystallize with the CePt₃B-type with a random distribution of Ce and Th atoms in positions 1(b) (1/2, 1/2, z) of the noncentrosymmetric space group P4mm. Th-doping results in a rapid suppression of the superconductivity. The alloy with x = 0.02 shows the onset of superconducting state at T_c = 400 mK, while that with x = 0.04 remains in normal metallic state at least down to 70 mK.     

Synthesis and structure determination of In3TeO3F7: An indium oxyfluorotellurate IV derived from W bronze structure with Te in hexagonal tunnels

After InTeO₃F and InTe₂O₅F recently described, a new compound In₃TeO₃F₇ is characterized in the In-Te^IV-O-F system. The crystal structure was determined by single X-ray diffraction and refined to R₁ = 0.028. In₃TeO₃F₇ crystallizes in orthorhombic space group Cmmm, a = 7.850(2) Å, b = 27.637(6) Å, c = 4.098(1) Å, V = 889.1(4) Å³ and Z = 4. Its structure consists of the stacking, via vertices, of identical layers composed of InF₆ and InO₂F₄ octahedra sharing corners and of InO₄F₃ pentagonal bipyramids sharing edges and vertices. The Te cations statistically occupy one or the other of two close sites located inside tunnels delimited by the In polyhedra and are bonded to F anions located in the same tunnels.The structure can be considered as an intergrowth of parallel strips of MIn₃F₁₀ and hexagonal tungsten bronze (c)-types. It is compared to other structures such as the bronze Sb_0.157WO₃, TeMo₅O₁₆ and Sb₂Mo₁₀O₃₁, phases also comprising Te⁴⁺ or Sb³⁺ inside hexagonal tunnels. The electronic lone pair of Te⁴⁺ is stereochemically active and a perfect O/F ordering occurs on the anionic sites.     

Effect of Ta seed layer on crystalline structure and magnetic properties in an exchange-biased Co/IrMn system

Ta-seeded and un-seeded layers of a top-configuration Co/IrMn system were deposited onto glass substrate by DC sputtering. Three sets of deposition conditions for Co(50 Å)/IrMn(t_IrMn Å) and Co(t_Co Å)/IrMn(90 Å), where t_IrMn = 15, 30, 60, 90, 110, and 150 Å, and t_Co = 15, 25, 50, 75, 100, 125, and 150  Å, were: condition (a) substrate temperature (T_s) was kept at room temperature (RT). Condition (b) T_s set to RT, with in-plane magnetic field, H = 500 Oe. In condition (c), condition (b) was followed by post-deposition annealing in the magnetic field at T_A = 250 °C for 1 h, then field cooled to RT. X-ray diffraction (XRD) patterns and grazing incidence scans revealed maximum IrMn (1 1 1) texture to occur for post-deposition annealed Ta seed layer samples. The IrMn (1 1 1) texture-effect significantly influences magnetic properties, including exchange-biasing field (H_ex), interfacial energy (J_k), and coercivity (H_c). The Ta seed layer also significantly influences magnetic properties. Adding a Ta seed layer to the Co/IrMn system increases H_ex, because of the IrMn (1 1 1) texture. For Ta-seeded Co/IrMn under condition (c), H_ex tended to saturate for t_IrMn ≥ 90 Å. Under conditions (a) and (b), H_ex decreased with increasing t_IrMn for t_IrMn ≥ 90 Å. H_ex values for all un-seeded Co/IrMn systems increased with t_IrMn. J_k versus t_IrMn plot is proportional only to H_ex in the Ta-seeded and un-seeded layers of a top-configuration Co/IrMn system, due to the interfacial energy formula, t_Co is fixed, and saturation magnetization (M_s) of the Co layer is constant. Results for the Ta-seeded system showed a strong relationship between H_c and t_IrMn, due to coupling-decoupling interactions between Co spin, and IrMn layers close to the Co/IrMn interface. The H_ex versus t_Co result shows that the H_ex is proportional to (1/t_Co). The H_ex values with the Ta seed layer are almost slightly larger than those without a Ta seed-layer. The dependence of J_k on t_Co is similar to the trend in M_s on t_Co, J_k tends to saturate slowly as t_Co increases. Surface pinning occurred in all systems, revealing an inverse relation between H_c and t_Co. Removing the Ta seed-layer weakens IrMn (1 1 1) texturing, reducing H_ex. The maximum observed H_ex and J_k values were 205 Oe and 0.11 erg/cm², respectively.     

Tetragonal-cubic phase boundary in nanocrystalline ZrO2-Y2O3 solid solutions synthesized by gel-combustion

By means of synchrotron X-ray powder diffraction (SXPD) and Raman spectroscopy, we have detected, in a series of nanocrystalline and compositionally homogeneous ZrO₂-Y₂O₃ solid solutions, the presence at room temperature of three different phases depending on Y₂O₃ content, namely two tetragonal forms and the cubic phase. The studied materials, with average crystallite sizes within the range 7-10 nm, were synthesized by a nitrate-citrate gel-combustion process. The crystal structure of these phases was also investigated by SXPD. The results presented here indicate that the studied nanocrystalline ZrO₂-Y₂O₃ solid solutions exhibit the same phases reported in the literature for compositionally homogeneous materials containing larger (micro)crystals. The compositional boundaries between both tetragonal forms and between tetragonal and cubic phases were also determined.     

Effect of ZrO2 on corrosion behaviour of chromium coatings

To study the effect of ZrO₂ particles on corrosion behaviour of Cr coating, steel samples were plated in Cr(VI) baths without and with ZrO₂. The corrosion behaviour of plated samples was studied at different exposure times in a solution containing 0.01 mol l⁻¹ H₂SO₄ + 0.5 mol l⁻¹ Na₂SO₄ using cyclic voltammetry and impedance spectroscopy. The equivalent circuit model R_e(Q_cR_pore)(Q_s[OR_s]) was proposed to fit the corrosion process and the parameters Y₀(Q_c),Y₀(Q_s) and R_pore reflecting corrosion behaviour of samples were evaluated. From the results, it was found that samples plated in bath containing ZrO₂ exhibited improved protective properties as a result of the structural characteristics of the coatings obtained; namely, the size and shape of pores.