Synthesis, structure and luminescent properties of Lu(PO3)3

A new structural type of rare earth metaphosphate, Lu(PO₃)₃, was prepared from high-temperature solution, of which the crystal structure was solved in S.G. of Cc (No.9) and Z = 4 with unit cell dimensions of a = 13.972(3) Å, b = 6.6710(13) Å, c = 9.958(2) Å and β = 127.36(3)°. In Lu(PO₃)₃, [LuO₆] octahedra connect with the non-bridging oxygens on (PO₃)_n infinite zigzag chains that extended along c-axis. The VUV and X-ray excited luminescent properties of undoped and Ln³⁺ (Ln = Ce, Eu, Tb) doped samples were examined, from which the optical band gap was estimated to be 8.3 eV. Besides, in the undoped sample a STE emission within 320–480 nm was observed, which probably be related to oxygen defects. However, in the Lu(PO₃)₃:Ce sample the Ce³⁺ emission was weak and STE emission was totally quenched under hard X-ray excitation.     

Crystal structure and characterization of [2,5-(CH3O)2C6H3NH3]4P4O12·2H2O

The preparation, crystal structure, TG–DTA analysis and spectroscopy investigation are reported for the 2,5-dimethoxy phenyl ammonium cyclotetraphosphate dihydrate [2,5-(CH₃O)₂C₆H₃NH₃]₄P₄O₁₂·2H₂O. This new compound is triclinic P with unit cell dimensions: a = 7.438(5) Å, b = 11.841(7) Å, c = 12.354(4) Å,  = 96.61(4)°, β = 98.35(4)°, γ = 102.60(6)°, Z = 1 and V = 1038.0(1) Å³. Its crystal structure has been determined and refined to R = 0.049, with 5128 independant reflections. The structure can be described by rows of P₄O₁₂ ring anions along the a axis; between these rows are located the organic groups, connected to them by hydrogen bonds.     

Deposition and dielectric properties of CaCu3Ti4O12 thin films on Pt/Ti/SiO2/Si substrates using pulsed-laser deposition

CaCu₃Ti₄O₁₂ (CCTO) thin films were successfully deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates using pulsed-laser deposition technique. The crystalline structure and the surface morphology of the CCTO thin films were greatly affected by the substrate temperature and oxygen pressure. Thin films with a (2 2 0) preferential orientation were obtained at the substrate temperature above 700 °C and oxygen pressure above 13.3 Pa. The 480-nm thin films deposited under 720 °C and 26.6 Pa have a fairly high dielectric constant of near 2000 at 10 kHz and room temperature. The values of the dielectric constant and loss and their temperature-dependence under different frequency are comparable with those obtained in the epitaxial CCTO films grown on oxide substrates.     

Raman scattering study on ferroelectric (Ba0.32Sr0.68)2Nb2O7 ceramics

Raman scattering technique was applied to examine the Ba-doping effect to the two low temperature phase transitions of Sr₂Nb₂O₇ (SN) in the temperature range from −190 to 600 °C. The line shape of Raman spectra can be well fitted by multidamped harmonic oscillator model. We did not observe any soft mode related to the two low temperature phase transitions corresponding to those of the pure SN. It is correlated to the disappearance of the incommensurate phase in (Ba_0.32Sr_0.68)₂Nb₂O₇ ceramics. However, the temperature dependence behavior of the three low frequency modes indicates another new structural phase transition around 270 °C. It is considered that the reduction of the interlayer interaction caused by partial replacement of Sr-site by Ba-site, whose ionic radius is larger than that of Sr, may be the reason for the disappearance of the incommensurate phase transition in (Ba_0.32Sr_0.68)₂Nb₂O₇ ceramics.     

Crystal structure and spectroscopic studies of NaGd(PO3)4

Single crystals of gadolinium–sodium polyphosphate NaGd(PO₃)₄ were grown for the first time using a flux method and characterized by X-ray diffraction. This phosphate crystallizes in a monoclinic system with P2₁/n space group and with the following unit-cell dimensions: a = 9.767(3) Å, b = 13.017(1) Å, c = 7.160(2) Å, β = 90.564(5)°, V = 910.3(4) Å³ and Z = 4. The crystal structure was solved from 3451 X-ray independent reflections with final R(F²) = 0.0219 and R_w(F²) = 0.056 refined with 164 parameters (). The atomic arrangement can be described as a long chain polyphosphate organization. Two infinite (PO₃)∝ chains with a period of eight tetrahedra run along the [0 1 1] direction. The structure of NaGd(PO₃)₄ consists of GdO₈ polyhedra sharing oxygen atoms with phosphoric group PO₄. Each Na⁺ ion is bonded to eight oxygen atoms.     

Al2O3 formation on Si by catalytic chemical vapor deposition

Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al₂O₃) thin films on silicon (Si) crystals using N₂ bubbled tri-methyl aluminum [Al(CH₃)₃, TMA] and molecular oxygen (O₂) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min⁻¹ at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10¹² cm⁻², small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10⁻⁷ A cm⁻² at a gate bias of 1 V.     

Carburization performance of Incoloy 800HT in CH4/H2 gas mixtures

Carburization performance of Incoloy 800HT has been studied after cyclic and isothermal exposures to CH₄/H₂ carburizing gas mixtures at high temperatures for 500 h. At 800 °C in 2% CH₄/H₂, Incoloy 800HT suffered external oxidation and carburization, the external continuous layer of reaction products consists primarily of Cr₇C₃, Mn_1.5Cr_1.5O₄, and FeCr₂O₄ with Fe(Cr, Al)₂O₄ as a minor phase. At 1100 °C in 10% CH₄/H₂, external carburization did not occur likely due to high carbon dissolution in the alloy substrate at this temperature. A thermodynamic analysis indicated that 1000 °C was an approximate critical temperature, below which the environment should result in mixed oxidizing/carburizing behavior, while above this temperature reducing carburizing behavior should occur. The experimental results approximately agree with the thermodynamic analysis. Metal dusting was not observed under highly carburizing conditions (a_C>1). The size and morphology of Cr-rich phases (or Cr-carbides) are both temperature- and time-dependent, while the external continuity is more temperature-dependent rather than time-dependent.     

Growth of calcium carbonate by the atomic layer chemical vapour deposition technique

Thin films of CaCO₃ (calcite) have been grown with the atomic layer chemical vapour deposition (ALCVD) technique, using Ca(thd)₂ (Hthd=2,2,6,6-tetramethylheptan-3,5-dione), CO₂, and ozone as precursors. Pulse parameters for the ALCVD-type growth are found and self-limiting reaction conditions are established between 200 and 400 °C. Calcium carbonate films have been deposited on soda-lime glass, Si(100), -Al₂O₃(001), -Al₂O₃(012), -SiO₂(001), and MgO(100) substrates. The observed textures were: in-plane oriented films with [100](001)CaCO₃ [100](001)Al₂O₃ and [100](001)CaCO₃[110](001)Al₂O₃ on -Al₂O₃(001), amorphous films on -Al₂O₃(012) when grown at 250 °C, and columnar oriented films on soda-lime glass, Si(001), -SiO₂(001), and MgO(100) substrates with (00l) and (104) parallel to the substrate plane at 250 and 350 °C, respectively. The film topography was studied by atomic force microscopy and AC impedance characteristics were measured on as-deposited films at room temperature. The films were found to be insulating with a dielectric constant (_r) typically approximately 8. Thin films of CaO were obtained by heat treatment of the carbonate films at 670 °C in a CO₂-free atmosphere, but the thermal decomposition led to a significant increase in surface roughness.     

Growth, thermal and optical properties of Yb:GdYAl3(BO3)4 crystal

Single crystal of Yb:GdYAl₃(BO₃)₄(Yb:GdYAB) has been grown by the flux method. The structure of Yb:GdYAB crystal has been determined by X-ray diffraction analysis. The experiment show that the crystal has the same structure as that of YAl₃(BO₃)₄ crystal and its unit cell constants have been measured to be a = 9.30146 Å, c = 7.24164 Å, Vol = 542.59 Å³. The absorption and fluorescence spectrum of Yb:GdYAl₃(BO₃)₄ crystal have also been measured at room temperature. In the absorption spectra, there are two absorption bands at 938 nm and 974 nm, respectively, which is suitable for InGaAs diode laser pumping. In the fluorescence spectra, there are two fluorescence peaks at 992 and 1040 nm. The thermal properties of Yb:GdYAl₃(BO₃)₄ crystal have been studied for the first time. The thermal expansion coefficient along c-axis is almost 5.4 times larger than that along a-axis. The specific heat of the crystal has been measured to be 0.77 J/g °C at room temperature. The calculated thermal conductivity is 5.26 Wm⁻¹ K⁻¹ along a-direction.     

Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol–gel route was investigated for preparation of epitaxial La_0.5Sr_0.5CoO₃ (LSCO) films on 100 SrTiO₃ (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min^− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al₂O₃ substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of a_c = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.     

Effect of SnO2 on the photocatalytical properties of TiO2 films

TiO₂/SnO₂ thin films with different tin atomic percentages were successfully prepared on glass substrates by the spray pyrolysis method from an alcoholic solution of TiO[C₅H₇O₂]₂ with different concentrations of SnCl₄. The TiO₂/SnO₂ thin films prepared at 450 °C presented the anatase phase in polycrystalline configuration from %Sn = 0 in the starting solution up to %Sn = 20, at higher tin content the films present an amorphous configuration. The resulting thin films have a homogeneous surface structure with some porosity. The photocatalytical properties of the films were evaluated with the degradation of methylene blue. The products of the degradation reaction were identified by ¹H nuclear magnetic resonance and the film properties were studied by atomic force microscopy, scanning electron microscopy, UV–Vis spectroscopy, and X-ray diffraction.     

Direct liquid injection metal-organic chemical vapor deposition of HfO2 thin films using Hf(dimethylaminoethoxide)4

Hf(OCH₂CH₂NMe₂)₄, [Hf(dmae)₄] (dmae=dimethylaminoethoxide) was synthesized and used as a chemical vapor deposition precursor for depositing Hf oxide (HfO₂). Hf(dmae)₄ is a liquid at room temperature and has a moderate vapor pressure (4.5 Torr at 80 °C). It was found that HfO₂ film could be deposited as low as 150 °C with carbon level not detected by X-ray photoelectron spectroscopy. As deposited film was amorphous but when the deposition temperature was raised to 400 °C, X-ray diffraction pattern showed that the film was polycrystalline with weak peak of monoclinic (020). Scanning electron microscope analysis indicated that the grain size was not significantly changed with the increase of the annealing temperature. Capacitance–voltage measurement showed that with the increase of annealing temperature, the effective dielectric constant was increased, but above 900 °C, the effective dielectric constant was decreased due to the formation of interface oxide. For 500 Å thin film, the dielectric constant of HfO₂ film annealed at 800 °C was 20.1 and the current–voltage measurements showed that the leakage current density of the HfO₂ thin film annealed at 800 °C was 2.2×10⁻⁶ A/cm² at 5 V.     

Sol–gel synthesis and luminescence of unexpected microrod crystalline Ca5La5(SiO4)3(PO4)3O2:Dy phosphors employing different silicate sources

Ca₅La₅(SiO₄)₃(PO₄)₃O₂ doped with Dy³⁺ were synthesized by sol–gel technology with hybrid precursor employed four different silicate sources, 3-aminopropyl-trimethoxysilane (APMS), 3-aminopropyl-triethoxysilane (APES), 3-aminopropyl-methyl-diethoxysilane (APMES) and tetraethoxysilane (TEOS), respectively. The SEM diagraphs show that there exist some novel unexpected morphological structures of microrod owing to the crosslinking reagents than TEOS as silicate source for their amphipathy template effect. X-ray pictures confirm that Ca₅La₅(SiO₄)₃(PO₄)₃O₂:Dy³⁺ compound is formed by a pure apatitic phase. The Dy³⁺ ions could emit white light in Ca₅La₅(SiO₄)₃(PO₄)₃O₂ compound, and the ratio of Y/B is 1.1, when the Dy³⁺ doped concentration is 1.0 mol%.     

Processing, microstructure and properties of C40 Mo(Si,Al)2/Al2O3 composites

The C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composites were prepared by spark plasma sintering (SPS) of mechanically alloyed (MA) powders. The Mo(Si_0.75Al_0.25)₂/0–20 vol.% Al₂O₃ materials, showing micron and submicron composite structure, possess a hardness of 13.9–14.6 GPa but a poor toughness of 1.78–1.80 MPa m^1/2. The addition of 30 vol.% Al₂O₃ leads to the formation of the micron C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composite with an intergranular distribution of Al₂O₃, that results in a drop of the hardness to 10.2 GPa and an improvement of the toughness to 3.67 MPa m^1/2. The transition of the cleavage facets to the intergranular fracture with the addition of Al₂O₃ is assumed as the main toughening mechanism.     

Consolidation behavior of L12 phase (Al + 12.5 at.% Cu)3Zr powder with nanocrystalline structure during CIP and subsequent sintering

The mechanically alloyed (Al + 12.5 at.% Cu)₃Zr powders were consolidated by cold isostatic pressing (CIP) and subsequent sintering. Effects of CIP pressure and sintering temperature on the stability of metastable L1₂ phase and nanocrystalline structure were investigated. Before sintering, the powders were CIPed at 138, 207, 276, and 414 MPa. The relative densities of the CIP compacts were not greatly affected by the CIP pressure. However, the L1₂ phase of the specimen CIPed at pressures greater than 276 MPa was partially transformed into D0₂₃. The optimum consolidation conditions for maintaining L1₂ phase and nanocrystalline microstructure were determined to be CIP at 207 MPa and sintering at 800 °C for 1 h for which the grain size was 34.2 nm and the relative density was 93.8%. Full density specimens could be prepared by sintering above 900 °C, however, these specimens consisted of L1₂ and D0₂₃ phases. The grain sizes of all the specimens were confirmed by TEM and XRD, and were found to be less than 40 nm. This is one of the smallest grain sizes ever reported in trialuminide intermetallic compounds.     

La2Zr2O7 films on Cu–Ni alloy by chemical solution deposition process

Films of La₂Zr₂O₇ (=LZO) have been formed by chemical solution deposition technique (CSD) on new bi-axially textured Cu–Ni alloy tapes based on rolled constantan (Cu₅₅Ni₄₅) Rabits. The precursor used was acetylacetonates treated in propionic acid (0.1–0.87 mol/l) and then deposited by spin-coating. The LZO film starts to crystallize above 850 °C, the film nucleates bi-axially textured on the substrate (with unit cell axis rotated 45° from those of the substrate). The top part of the film is not textured even after long annealing time at 1100 °C, but the interfacial part is bi-axially textured. Thus, synthesis of bi-axially textured films on Cu₅₅Ni₄₅ Rabits seems possible but more works are needed to optimize its properties.     

Synthesis, structure refinement and characterization of tetrahydrated acid gadolinium diphosphate HGdP2O7·4H2O

Synthesis and single crystal structure are reported for a new gadolinium acid diphosphate tetrahydrate HGdP₂O₇·4H₂O. This salt crystallizes in the monoclinic system, space group P2₁/n, with the following unit-cell parameters: a = 6.6137(2) Å, b = 11.4954(4) Å, c = 11.377(4) Å, β = 87.53(2)° and Z = 4. Its crystal structure was refined to R = 0.0333 using 1783 reflections. The corresponding atomic arrangement can be described as an alternation of corrugated layers of monohydrogendiphosphate groups and GdO₈ polyhedra parallel to the () plane. The cohesion between the different diphosphoric groups is provided by strong hydrogen bonding involving the W4 water molecule.

IR and Raman spectra of HGdP₂O₇·4H₂O confirm the existence of the characteristic bands of diphosphate group in 980–700 cm⁻¹ area. The IR spectrum reveals also the characteristic bands of water molecules vibration (3600–3230 cm⁻¹) and acidic hydrogen ones (2340 cm⁻¹). TG and DTA investigations show that the dehydration of this salt occurs between 79 and 900 °C. It decomposes after dehydration into an amorphous phase. Gadolinium diphosphate Gd₄(P₂O₇)₃ was obtained by heating HGdP₂O₇·4H₂O in a static air furnace at 850 °C for 48 h.     

Preparation and optical properties of sol–gel derived Er-doped Al2O3–Ta2O5 films

Thin films of the system xAl₂O₃–(100 − x)Ta₂O₅–1Er₂O₃ were prepared by a sol–gel method and a dip-coating technique. The influences of the composition and the crystallization of the films on Er³⁺ optical properties were investigated. Results of X-ray diffraction indicated that the crystallization temperature of Ta₂O₅ increased from 800 to 1000 °C with increased values of x. In crystallized films, the intensities of the visible fluorescence and upconversion fluorescence tend to decrease with an increase in x values, due to the high phonon energy of Al₂O₃; the strongest fluorescence is observed in a crystallized film for x = 4 heat treated at 1000 °C. In amorphous films obtained by heat treatment at relatively low temperatures the Er³⁺ fluorescence could not be observed because strong fluorescence from organic residues remaining in the films thoroughly covered the Er³⁺ fluorescence. On the other hand, the Er³⁺ upconversion fluorescence in the amorphous films was observed to be stronger than that in the crystallized films. The strongest upconversion fluorescence is observed in an amorphous film for x = 75 heat treated at 800 °C.     

Formation of a highly oriented FeO thin film by phase transition of Fe3O4 and Fe nanocrystallines

A highly oriented FeO thin film was formed from a Fe₃O₄ thin film containing Fe nanocrystallines by post-annealing at 600°C. Fe₃O₄ thin films were grown on Si(100) substrates by ion beam sputter deposition under oxygen ambient. The stoichiometry of the iron oxide thin film could be precisely controlled by in situ X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) pattern of the Fe₃O₄ thin film grown at substrate temperature of 300°C showed a mixed phase of Fe₃O₄ and Fe nanocrystallines with a preferred orientation (110). However, the mixed phase was converted to a highly oriented FeO(200) phase by post-annealing at 600°C. This could be inverted as a result of Ostwald ripening of the Fe₃O₄ and Fe nanocrystallines.     

Synthesis, phase transformation and dielectric properties of sol–gel derived Bi2Ti2O7 ceramics

Sol–gel derived Bi₂Ti₂O₇ ceramic powders have been prepared from methoxyethoxides of bismuth and titanium (molar ratio of Ti/Bi = 1.23 and water/alkoxides = 1.31). The Bi₂Ti₂O₇ phase was stable at a low temperature (700 °C), but it then transformed into mixed phases of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ at 850–1150 °C. The single phase of Bi₂Ti₂O₇ reoccurred at 1200 °C. Dielectric properties and ferroelectric behavior of samples sintered at 1150 and 1200 °C were examined. Under frequency of 1 MHz, samples sintered at 1150 and 1200 °C had a dielectric constant of 101.3 and 104.2, and a loss tangent of 0.0193 and 0.0145, respectively. Only the sample sintered at 1150 °C showed ferroelectric behavior, where remanent polarization is 3.77 μC cm⁻² and coercive field is 24 kV cm⁻¹. Thus, the Bi₂Ti₂O₇ did not exhibit ferroelectricity, but the mixed phase of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ did.