Lewis Acid–Base Adduct Me3Sb–Ga(t-Bu)3

Abstract  

The simple Lewis acid–base adduct Me₃Sb–Ga(t-Bu)₃ 1 was prepared by reaction of t-Bu₃Ga and SbMe₃ in 1:1 M ratio. 1 was fully characterized by multinuclear NMR spectroscopy (¹H, ¹³C). In addition, its solid state structure was determined by single crystal X-ray diffraction studies. 1 is monoclinic, space group P2₁ /n with a = 8.4895(2) ?, b = 12.9303(4) ?, c = 17.9976(5) ?, β = 97.472(2)° and Z = 4.     

The K2S2O8–KOH photoetching system for GaN

A recently developed photoetching system for n-type GaN, a KOH solution containing the strong oxidizing agent potassium peroxydisulphate (K₂S₂O₈), was studied in detail. By careful selection of the etching parameters, such as the ratio of components and the hydrodynamics, two distinct modes were defined: defect-selective etching (denoted by KSO-D) and polishing (KSO-P). Both photoetching methods can be used under open-circuit (electroless) conditions. Well-defined dislocation-related etch whiskers are formed during KSO-D etching. All types of dislocations are revealed, and this was confirmed by cross-sectional TEM examination of the etched samples. Extended electrically active defects are also clearly revealed. The known relationship between etch rate and carrier concentration for photoetching of GaN in KOH solutions was confirmed for KSO-D etch using Raman measurements. It is shown that during KSO-P etching diffusion is the rate-limiting step, i.e. this etch is suitable for polishing of GaN. Some constraints of the KSO etching system for GaN are discussed and peculiar etch features, so far not understood, are described.     

Thermodynamics of the Al–Ga–N2 system

The thermodynamic properties of the Al–Ga–N₂ system under high N₂ pressure up to 10 kbar and 1800 °C are investigated. On the basis of the experimental p–T growth conditions for (Al,Ga)N crystals, the standard Gibbs free energy as well as the standard enthalpy and entropy of formation of the Al_xGa_1−xN crystals as a function of composition x were calculated. The a_N2–T and x–T phase diagrams for (Al,Ga)N are presented.     

Controlling metal–insulator transition in the hetero-epitaxial VO2/TiO2 bilayer grown on Al2O3

Hetero-epitaxial VO₂/TiO₂ bilayers were synthesized on Al₂O₃ substrates by using pulsed laser deposition, and their physical properties with the changes of oxygen pressure and the substrate orientation were investigated. A metal–insulator transition of the VO₂ was observed only in a narrow oxygen pressure range of 5–20 mTorr. As the oxygen pressure increased, X-ray diffraction peak for the (2 0 0)VO₂ shifted to a lower 2θ position, while the metal–insulator transition temperature (T_MI) decreased by ∼7 K. On the other hand, T_MI was largely varied with substrate orientation. The (2 0 0)VO₂/TiO₂ on the c-plane sapphire showed the highest T_MI of about 350 K, while the (0 0 2)VO₂/TiO₂ on the m-plane sapphire displayed the lowest T_MI of about 310 K. The (1 0 1)VO₂/TiO₂ on the r-plane and the a-plane exhibited T_MI∼340 and 330 K, respectively. The observed variations of T_MI with the oxygen pressure and substrate orientation were presumably due to the change in oxygen content of the VO₂ layer and/or in lattice strain.     

On the Two Closely Related Phases of [Ru(C5Me5)(η6-1,3-(Me2NCH2)2C6H4)](BF4) and the Reversible Solid–Solid Order–Disorder Phase Transition

Abstract  

Crystals of the complex [Ru(C₅Me₅)(η⁶-1,3-(Me₂NCH₂)₂C₆H₄)](BF₄) have been examined over the temperature range 150–300 K via X-ray diffraction measurements. This study shows that the Ru complex is a two-phase system in this T-range and the solid–solid transition is reversible. At 150 K, phase II (P2₁/c, Z′ = 4) is ordered and non-merohedrally twinned, a = 16.4396 (9) ?, b = 17.3226 (4) ?, c = 32.1874 (11) ?, β = 91.375 (2)°. At 295 K, phase I (Pbca, Z′ = 1) is disordered, a = 8.5071 (3) ?, b = 17.1567 (3) ?, c = 32.8250 (8) ?. The relationship between the two phases is obvious because the packing remains similar in the two phases. The greatest structural changes between the two phases are found in the rows of adjacent cations [Ru(C₅Me₅)(η⁶-1,3-(Me₂NCH₂)₂C₆H₄)]⁺ packed along the a direction. These rows are ordered in phase II but are disordered in phase I. The phase transition is first order. Significant changes in thermal motion for the cations are considered as being the driving force for the occurrence of this phase transition.     

Sol–gel preparation and photoluminescence properties of Ce-activated Y3Al5O12 nano-sized powders

Trivalent cerium-doped yttrium aluminum garnet (YAG:Ce³⁺) nanoparticles were successfully prepared by a facile sol–gel technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were used to characterize the as-prepared phosphors. Well-crystallized fine nanoparticles were obtained at 1000 °C. Single-crystal nanoparticles with irregular shapes were obtained, with crystallite sizes ranging between 20 and 60 nm. PL intensity of the particles increased monotonically with decreasing Ce doping concentration and showed the maximum value at 0.1 at%.     

Infrared transmission of (R2O OR R’O)–(TiO2, Nb2O5 OR Ta2O5)-Al2O3 glasses

The new families of aluminate glasses obtained by the present authors from their melts in the systems K₂O–Ta₂O₅–Al₂O₃, Na₂O–K₂O–Ta₂O₅–Al₂O₃, K₂O –Cs₂O– Ta₂O₅–Al₂O₃, K₂O–Nb₂O₅–Al₂O₃, Na₂Oz.sbnd;K₂O–TiO₂–Al₂O₃, BaO–TiO₂–Al₂O₃, BaO–ZrO₂–TiO₂–Al₂O₃ and Na₂O–K₂O–BaO–ZrO₂–Ta₂O₅–TiO₂ –Al₂O₃ showed high transmissions of visible and infrared (IR) radiation ranging from 0.4 to about 6 μm, as well as high refractive indices up to 2.0. Their physical and chemical properties such as glass-forming ability, softening temperature, hardness and hygroscopicity were comparable to conventional silicate glasses. These properties are useful for IR applications. The cause of the high IR transmission of the aluminate glasses was interpreted in terms of the masses of the constituent cations and the single bond strengths of the cations with oxygen ions.     

Determination of the supersaturation in the LiIO3–HIO3–H2O system using a refractive index value at near saturation concentration

The exact determination of supersaturation is essential for the studies of crystal growth processes in solutions. Due to peculiarities in the solubility of LiIO₃, the refractive index of the solution is chosen as a measure of the supersaturation instead of undercooling. The experimental setup is based on a refractometer and a special setup to create supersaturation in the cuvette by means of successive evaporation of small amounts of solvent. The refractive index is measured at different solution concentrations and pH and the data are correlated as dependences of concentration and pH on the refractive index. The accuracy of the method and the adequacy of the model are discussed.     

X-ray diffraction study of p -(alkoxybenzylidene)- p ′-toluidines C2H5O-C6H4-CH=N-C6H4-CH3 and C4H9O-C6H4-CH=N-C6H4-CH3

The molecular and crystal structures of two p-alkoxybenzylidene)-p′-toluidines C₂H₅O-C₆H₄-CH=N-C₆H₄-CH₃ (1) and C₄H₉O-C₆H₄-CH=N-C₆H₄-CH₃ (2) are determined by X-ray diffraction. Crystals 1 and 2 contain four and two crystallographically independent molecules, respectively. In 1, the geometry of the independent molecules is almost identical. In 2, the independent molecules differ in the conformation of the alkyl chain, which is disordered in one of them. An analysis of the crystal packing of 2 reveals the alternation of spacious layers formed by loosely packed aliphatic fragments of molecules and layers of closely packed aromatic fragments, which ensures the formation of the mesogenic phase in the course of melting of crystals 2. In crystal 1, loose aliphatic layers are absent. Original Russian Text ? L.G. Kuz’mina, N.S. Kucherepa, M.N. Rodnikova, 2008, published in Kristallografiya, 2008, Vol. 53, No. 6, pp. 1072–1078.     

X-ray diffraction study of p -(alkoxybenzylidene)- p ′-toluidines C5H11O-C6H4-CH=N-C6H4-CH3 and C8H17O-C6H4-CH=N-C6H4-CH3

The molecular and crystal structures of two p-(alkoxybenzylidene)-p′-toluidines C₅H₁₁O-C₆H₄-CH=N-C₆H₄-CH₃ (1) and C₈H₁₇O-C₆H₄-CH=N-C₆H₄-CH₃ (2), which form the nematic phase upon melting, is determined by X-ray diffraction. The geometry of the benzylideneaniline fragments in molecules 1 and 2 is actually identical. The crystal packings of 1 and 2 are characterized by the alternation of layers formed by loosely packed aliphatic fragments of molecules and layers of closely packed aromatic fragments. The packing in the aromatic regions of 1 follows the parquet pattern. The crystal packing of 2 has a stacking structure, which is formed by π-stacking dimers superimposed on one another. The formation of the mesogenic phase upon melting of crystals 1 is due to the disturbance of the structurality of loose aliphatic layers with retention of the structure of the aromatic regions, which are stabilized by the cooperative effect of weak directed C-H ··· π-system interactions. The mesogenic phase of crystals 2 is formed upon melting as a consequence of the retention of the structure of π-stacking dimers. Original Russian Text ? L.G. Kuz’mina, N.S. Kucherepa, M.N. Rodnikova, 2008, published in Kristallografiya, 2008, Vol. 53, No. 6, pp. 1079–1085.     

Synthesis and Structural Characterization of Two New Layered Inorganic–Organic Hybrid Zinc Phosphites Templated by Cyclam: Zn(HPO3)2·0.5(C10H28N4) and Zn2(HPO3)3·0.5(C10H28N4)

Abstract  

Using 1,4,8,11-tetraazacyclotetradecane (cyclam) as a template, two new layered zincophosphites, Zn(HPO₃)₂·0.5(C₁₀H₂₈N₄) (1) and Zn₂(HPO₃)₃·0.5(C₁₀H₂₈N₄) (2), were synthesized and characterized by single crystal X-ray diffraction. The two new compounds crystallize in the triclinic system with the space group P − 1 and the cell parameters: a = 8.3130 ?, b = 8.7289 ?, c = 9.0055 ?, α = 106.90(1), β = 95.56(1), γ = 105.30(1), V = 592.31 ?³, Z = 2 for 1 and a = 9.0406 ?, b = 9.4234 ?, c = 9.4519 ?, α = 91.19(1), β = 100.73(1), γ = 106.85(1), V = 754.82 ?³, Z = 2 for 2. Both structures are described in terms of phosphometallic slabs hosting the cyclam cation.     

Al2O3掺杂对Ca0.2Sr0.05Li0.375Sm0.375TiO3微波介电性能的影响

采用固相烧结法制备了掺杂Al2O3的Ca0.2Sr0.05Li0.375Sm0.375Ti O3微波介质陶瓷。研究了Al2O3掺杂对Ca0.2Sr0.05Li0.375Sm0.375Ti O3的助烧效果、物相结构、显微组织和微波介电性能的影响规律。结果表明:Al2O3的添加降低了Ca0.2Sr0.05Li0.375Sm0.375Ti O3陶瓷的烧成温度,但对物相基本无影响。此外,高含量Al2O3的添加能促进晶粒细化。此体系陶瓷的最佳介电性能为:Al2O3含量为0.9wt%且烧成温度为1250℃时,εr=110.8、Q·f=4159.6 GHzτf=49.4 ppm/℃。     

Growth rate of α-calcium sulfate hemihydrate in K–Ca–Mg–Cl–H2O systems at elevated temperature

Kinetics of calcium sulfate hemihydrate (HH) crystal growth plays an important role in mineralization of calcium sulfate phases in nature. HH crystal growth and the conversion of calcium sulfate phases form the basis for the production and application of gypsum based building material. α-HH crystals have been grown in 3.74 M CaCl₂ solutions at a fixed initial ratio of calcium to sulfate under atmospheric pressure. The variations of sulfate ions were determined to obtain the α-HH crystal growth kinetics information. Effects of Mg²⁺ and K⁺ ions on α-HH growth were investigated to find an optimal composition of solution for α-HH preparation. The orders of α-HH growing in the CaCl₂ solution were found, in most cases, to be near 2.0 in presence or in absence of Mg²⁺ and K⁺ ions. Mg²⁺ ions enhance the growth of α-HH in CaCl₂ solution mainly due to initial supersaturation enhancing effects. K⁺ ions also improve the growth rate, which has been attributed to the reduction of interfacial energy. In a Ca (3.74 M)–Mg (0.20 M)–K (0.09 M) chlorides solution, the growth rate of α-HH increases with temperature from 80 to 100 °C, and the activation energy was calculated to be 40 kJ/mol.     

Bi4Si3O12-Bi4Ge3O12赝二元系统析晶行为及其晶体生长

本文采用固相合成方法制备了Bi4(GexSi1-x)3O12(BGSO)固溶体(x=0～0.4),研究了它的固溶特性和析晶行为。实验结果表明,不同组成混合料在900℃左右固相反应能生成BGSO纯相;XRD分析显示,在x=0～0.4区间内,Bi4Si3O12和Bi4Ge3O12可以完全互溶,其晶格常数随x的增加呈线性增长。采用坩埚下降法生长了x=0.15组成的BGSO混晶,获得了透明晶体,并测试了晶体的光学性能。     

Ba2Ti9O20-BaFe12O19复合陶瓷电磁性能的研究

本文采用流延成型法制备2-2型Ba2Ti9O20-BaFe12O19复合陶瓷。通过扫描电镜、能量散射光谱仪、X射线衍射、振动样品磁强计对复合陶瓷界面微观结构及磁、电性能进行了分析。结果表明:复合陶瓷的介电常数和介电损耗均大于单相Ba2Ti9O20,饱和磁化强度、剩余磁化强度均小于单相BaFe12O19,矫顽力大于单相BaFe12O19。随着烧结温度的升高,复合陶瓷的介电常数先增加后减小,介电损耗的变化则相反;饱和磁化强度、剩余磁化强度和矫顽力减小。在1180℃烧结4 h的复合陶瓷具有适合的磁、电性能:εr=115,tanδ=0.0054,Ms=21.9 A.m2/kg,Mr=12.5 A.m2/kg和Hc=63.0 kA/m。     

Invar effect in n-Nb2O5, αht-Nb2O5, and L-Nb2O5

An X-ray diffraction analysis of two commercial sets of niobium pentaoxide (Nb₂O₅) of Nbo-Pt grade has been performed. Each set reveals the coexistence of three modifications: n-Nb₂O₅, α_ht-Nb₂O₅, and L-Nb₂O₅. Anomalous behavior in the structural characteristics, with the occurrence of plateaus upon heating (the invar effect), is established for each phase. It is suggested that the coincidence of the temperature ranges with constant unit-cell parameters in Nb₂O₅ and complex Nb-containing oxides indicates the unified nature of the invar effect, which is related to the defect state of objects under study. Original Russian Text ? L.A. Reznichenko, V.V. Akhnazarova, L.A. Shilkina, O.N. Razumovskaya, S.I. Dudkina, 2009, published in Kristallografiya, 2009, Vol. 54, No. 3, pp. 517–526.     

Zn0.99Cu0.01Al2O4-SrTiO3微波陶瓷介电性能的研究

以分析纯Zn O、Cu O、Al2O3、Ti O2以及Sr CO3为原料,采用传统固相法制备了(1-x)Zn0.99Cu0.01Al2O4-x Sr Ti O3(ZCAST,x=0~0.045)微波介质陶瓷,利用X射线衍射仪、扫描电镜和网络分析仪对其结构、形貌和微波介电性能进行表征。研究了不同x值对ZCAST陶瓷相组成、显微结构以及微波介电性能的影响。结果表明,ZCAST陶瓷的体积密度、介电常数εr随着Sr Ti O3含量的增多而增大。当x=0.04具有最佳微波介电性能:介电常数εr=14.12,品质因数Q×f=28700 GHz,频率温度系数τf=-1.8×10-6/℃。     

Characterization and synthesis of Y0.9Ca0.1Ba1.8Sr0.2Cu3O7−δ via combining sol-gel and solid-state route

We applied the conventional sol-gel and solid-state reactions in this study to prepare double-substituted superconducting Y_0.9Ca_0.1Ba_1.8Sr_0.2Cu₃O_7−δ. The result and the effect of calcium and strontium doping on high-T_c compound Y-123 have been investigated. The precursor gel Ca-Ba-Sr-Cu-O was prepared by acetate-tartrate sol-gel route which involved hydrolysis and olation (polycondensation). Y_0.9Ca_0.1Ba_1.8Sr_0.2Cu₃O_7−δ was obtained by solid-state reaction between Y₂O₃ and Ca-Ba-Sr-Cu-O heated at 880 °C for 18 h with step cooling 50 °C/h until 450 °C. Without oxygen flow during the whole annealing process, the sample still showed good superconducting properties with T_c-zero close to 80 K. The presence of organic material in the sol-gel precursor Ca-Ba-Sr-Cu-O is nucleophile species, which is chemically reactive to Y₂O₃ during solid-state reaction thus enhance the diffusion rate. Moreover, -OH group in the precursor gel has ability to provide a sufficient amount of oxygen for the sample to stabilized the multicomponent superconductor.     

K0.5Na0.5NbO3掺杂对0.94Bi0.5Na0.5TiO3-0.06BaTiO3陶瓷储能性能的影响

采用传统固相反应法制备了K_0.5Na_0.5NbO₃(KNN)掺杂的无铅介电储能陶瓷BNT-BT-KNN,其组分配比为0.94Bi_0.5Na_0.5TiO₃-(0.06-x)BaTiO₃-xK_0.5Na_0.5NbO₃(BNT-BT+xKNN,x=0.00～0.04),并研究了KNN掺杂对BNT-BT基陶瓷材料晶相、微观结构、介电、铁电性能及储能的影响。结果表明：在1 150℃温度下烧成后的陶瓷样品具有纯的钙钛矿结构,且样品的晶粒均匀致密;介电温谱显示,添加KNN后的BNT-BT铁电陶瓷在T_m处的介电峰进一步宽化,表现出更好的温度稳定性和弛豫性;同时随着KNN掺杂量的增加,样品的电滞曲线(P-E曲线)逐渐由“宽胖型”向“细长型”转变,样品的剩余极化强度(P_r)逐渐降低,从而进一步提高了BNT-BT陶瓷的储能性能。在2 kV/mm的场...     

0.2wt% Bi2O3、CuO、B2O3对5Ca0.6La0.267TiO3-5Ca(Mg1/3Nb2/3)O3微波介质陶瓷的性能影响

采用传统的固相反应法,研究了三种烧结助剂Bi2O3、CuO、B2O3对5Ca0.6La0.267TiO3-5Ca(Mg1/3Nb2/3)O3微波介质陶瓷的烧结性能和介电性能的影响。实验结果表明,掺入0.2wt%的Bi2O3、CuO、B2O3产生了液相,有效地降低了体系的烧结温度。Bi2O3和CuO的加入没有改变烧结体的微观形貌,它们介电常数和品质因数随烧结温度的变化趋势和体积密度趋于一致,均在体积密度最大时最高。当温度大于1300℃时,加入0.2wt%B2O3试样有柱状晶体生成,并随着烧结温度的升高而增多,柱状晶体的存在可能促使Q×f值较大的提高,当烧结温度过高时(1350℃),由于柱状晶体过多使得烧结体不均匀导致Q×f值下降。Bi2O3、CuO、B2O3的加入没有改变烧结体的晶相组成,因此所有烧结体均有近零的温度系数。结果表明,加入0.2wt%B2O3的5Ca0.6La0.267TiO3-5Ca(Mg1/3Nb2/3)O3在1325℃烧结温度具有最佳的介电性能:εr=54.87,Q×f=55 726 GHz,τf=-0.6 ppm/℃。