Cleavage Mechanoluminescence in Crystals

When a crystal is cleaved, initially the mechanoluminescence (ML) intensity increases linearly with time, attains an optimum-value I_m at a particular value of timet_m, and then decays exponentially with time. Cleavage ML provides a new tool to determine the velocity, v of cracks in crystals, and it may be given by v = H/t_m, where H is the thickness of the crystal. Both, the peak ML intensity I_m and total ML intensity I_T increase linearly with the area of newly created surfaces A as well as with the surface charge density γ. The ML intensity decreases with temperature primarily due to the decrease in the surface charge density. Beyond a particular temperature, the surface charge density may decrease to such a value where the breakdown of gases and solids may not be possible and thereby the ML may not appear. Depending on the prevailing conditions either the ML emission resembling gas discharge or other types of the luminescence of solids, or that having these two characters may be obtained. There exists a good correlation between the theoretical and experimental results obtained for cleavage ML in crystals.     

Properties of oriented TTF-TCNQ thin films

Vapour deposited thin films of the organic molecular complex tetrathiafulvaliniumtetracyanoquinodimethane (TTF-TCNQ) are investigated by electrical and electronmicroscopical methods. Morphology studies by means of electron micrographs show, that the thin films up to thicknesses of 300 nm consist of small crystals of a size of 1.2 · 0.2 μm² (deposited on cleaved (100) faces of NaCl) or 15 · 2 μm² (on glass substrate). Dependend on deposition conditions and on material of the substrate thin films are produced with strong or statistic orientation of this crystals. Strong oriented thin films exhibit conductivities up to σ = 65 ω⁻¹ cm⁻¹ and activation energies of W_A = 0.02 eV. The found dependences of the conductivity on electrical field strength. temperature, and size of microcrystals are explained by a linear hopping model.     

An Unpredictable Reaction of <Emphasis Type="Italic">t</Emphasis>Bu<Subscript>2</Subscript>PHO·BCl<Subscript>3</Subscript> in the Presence of Water

Abstract  

When a benzene solution of tBu₂PHO·BCl₃ was exposed to air at room temperature, the phosphonium chloride [tBu₂PH₂]Cl was formed together with di-tert-butylphosphinic acid, tBu₂PO(OH). X-ray quality crystals of the hydrochloride [tBu₂PH₂]Cl·HCl were obtained from the reaction solution at room temperature. The hydrochloride [tBu₂PH₂]Cl·HCl crystallizes in the monoclinic space group P2₁ /m, a = 6.3012(7) ?, b = 6.8970(10) ?, c = 14.5011(15) ?, β = 99.376(9)°, V = 621.79(13) ?³, Z = 2, d _calcd = g cm⁻³ 1.165; R1 = 0.0510, wR2 = 0.1503 for 1,129 reflections with I > 2σ(I). The crystal was a non-merohedral twin with a contribution of 0.353(7) of the minor component. The structure is composed of discrete di-t-butylphosphonium cations and Cl anions. Both are located on a crystallographic mirror plane and are connected by P–H···Cl hydrogen bonds.     

Investigations on the growth kinetics of GP zones and a′R-precipitates in Al-Zn alloys

X-ray small-angle scattering (XSAS) and resistivity (R) measurements were particularly done with an Al-Zn (15 at·,%) alloy in rather wide ranges of both the ageing time t_a and ageing temperature T_a, in order to obtain information on the dependence of the growth exponent m of the l = β₀t^m growth law and the activation energy E_act on t_a and T_a. The XSAS-measurements yielded that within the range of the GUINIER radius r_G between 1 nm and 2 nm the growth is essentially retarded (m < 0.1) and for r_G > 2 nm m depends on T_a ranging from 0.15 to 0.23 with a maximum at 175°C. Reasons for these effects are discussed. The differences between the m-values obtained by means of XSAS-and TEM-measurements are explained by the distinctions of the two methods applied. The E_act taken from XSAS- and R-measurements show a remarkable increase with t_a. At the beginning of the decomposition E_act = (0.49 ± 0.05) eV holds well explainable by the migration of quenched-in VZn pairs, but at the end E_act = (1.05 ± 0.07) eV was found. This value was also obtained from TEM-investigations (growth of the length). It fits well the E_act of ZnV pairs in thermal equilibrium at T_a.     

Theoretical Approach to the Deformation-induced Luminescence in Metals

The present paper reports the mechanoluminescence (ML) produced during fracture of metals. The mechanism of ML in metals is based on the generation of holes during the decay of mobile dislocations on the surface and subsequent electron-hole radiative recombination. The following equation is derived for the transient ML intensity of the fracto-induced ML in metals . The above equation shows that I should be maximum for a particular value of time t. For β 〉 α, . This equation shows that I should decrease exponentially with time. For the fracto-induced ML in metals, t_M and I_m may be expressed by the following equations . The spectroscopy of ML in metals is also discussed. A good correlation is found between the theoretical and experimentals results.     

Zur Kenntnis des lithium-neodym-polyphosphates LiNd(PO3)4

LiNd(PO₃)₄ crystallized from a LiPO₃ flux exhibits (100) platelet or [001] prismatic habit, bot with pseudo-orthorhombic tracht. - Crystals are optically biaxial positive. Indices of refraction are nα = 1.6125; nβ = 1,6195 ± 0.0005 (λ = 589.3 nm); optic axial angle 2Vγ = 43°; maximum birefrigence δn = 12.7 · 10⁻³; birefrigence in (100) δn_a = 5.9 · 10⁻³.     

Growth of bulk zinc chalcogenide single crystals from the vapour phase and their use for laser screens of projection colour television

Results on ZnSe, ZnSe_xS_1−x and ZnS crystal growing from the vapour phase up to 7.5 cm³ in volume are described. Crystals were grown on sapphire, ZnS, ZnSe_xS_1−x and quartz glass substrates without a contact of the growing crystal with a growth ampoule and using the molten tin as a heating medium. Large high-purity crystals with a density of etch pits of 10³ cm⁻² were obtained They exhibited an effective exciton luminescence and rather high radiation efficiency (30 ± 10% for ZnSe at T = 77 K). This made it possible to use these crystals for fabricating laser screens for a cathode ray tube. The main laser parameters obtained on a ZnSe screen at T = 80 and 300 K using a 75 keV electron beam excitation are presented. The light power output reached 0.8 W at T = 80 K; this allowed to obtain a 10 cd · m⁻² TV image of 1.5 × 2 m² in area.     

Simulation of metastable zone width and induction time for a seeded aqueous solution of potassium sulfate

The metastable zone width (MSZW, ΔT_m) and induction time (t_ind) were determined with computer simulation for seeded batch crystallization of potassium sulfate from aqueous solution. The MSZW and induction time determined with simulation showed the same behavior as experimental values reported in the literature; log (ΔT_m) increased linearly with an increase in log R (R: cooling rate) and t_ind decreases in proportion to (ΔT)⁻ⁿ (ΔT: supercooling, n: nucleation order in the secondary rate expression of B=k_n(ΔT)ⁿ). The secondary nucleation parameters (k_n and n) were deduced both from the simulated MSZW and induction times by using the previously proposed model [J. Cryst. Growth, 2010, 312, 548–554]. The secondary nucleation rate calculated with the deduced parameters was in agreement with that calculated with the parameters input for simulation.     

Emissionselektronenmikroskopische Untersuchungen am Zweistoffsystem Niob-Eisen

Results from emission electron microscope investigations of thermal and mechanical behaviour of the Laves-phase NbFe₂ and of two-phase areas in the binary system Nb Fe are presented. The melting process of NbFe₂ samples with included μ-phase NbFe was observed in the emission microscope and supported the existence of a eutectic between both intermetallic compounds. The Laves-phase NbFe₂ was deformed plastically by a microhardness tester and also homogenously by a compressive device during electron microscope observations. Both yield stress and microhardness of NbFe₂ were measured as a function of temperature up to 1550 K. The relation between a critical temperature T₀ of the hardness-temperature curve and the melting temperature T_m was T₀/T_m = 0,64, in good agreement with results from other Laves-phases. During the heating of NbFe₂ samples a niobium oxide decoration structure appeared at residual air pressures from 1 · 10⁻⁶ torr to some 10⁻⁴ torr. The observed density of decoration points amounted to (1…5) · 10⁸ cm⁻². A discussion shows the possibility of a connection between decoration points and dislocations emerging from the crystal.     

The precipitation of alkaline-earth metal polymetaphosphate hydrate powders from aqueous solution. Nucleation and crystal growth processes,final precipitate compositions and crystal sizes

The precipitation of barium, strontium, calcium and magnesium polymetaphosphate hydrates was studied from aqueous solutions of initial metal salt concentrations from 0.001 to 3 M at 20 °C; equivalent sodium polymetaphosphate solutions were added to the alkaline-earth metal chloride solutions. Precipitate compositions were determined by chemical analysis, paper chromatography, potentiometric analysis, thermogravimetric and differential thermal analysis and infra-red spectrophotometry; final crystallite morphologies and sizes were studied by scanning electron microscopy and X-ray powder diffraction. Nucleation rates and nucleus numbers (at the end of the induction periods) were very high; crystal numbers varied from 10¹⁴ to 10¹⁵ at the critical concentrations to above 10¹⁷ per 1. solution. Crystal growth rates were also very high and varied as the fourth power of the initial metal salt concentration. High molecular-weight metal polymetaphosphate hydrates were precipitated from the more dilute solutions (0.001 to 0.025 M) while increasing amounts of the more soluble intermediate and low molecular-weight products were precipitated from the more concentrated solutions. Washing with cold water removed the tri- and tetralinear and cyclic phosphate products. The magnesium salts were not precipitated even from 3 M aqueous solutions. The precipitates from aqueous (NaPO₃(I))_n (n = 12) solutions had the compositions (BaP₂O₆ · 2.5 H₂O)₆, (SrP₂O₆ · 3 H₂O)_n and (CaP₂O₆ · 4 H₂O)_n while the magnesium salt precipitate from 20 percent aqueous acetone solution had the composition (MgP₂O₆ · 4 H₂O)_n, the precipitate n values varied from 19 to 13. The precipitates from aqueous (NaPO₃(II))_n (n = 20) solutions contained 0.5n to n additional adsorbed water molecules; these precipitate n values varied in turn from 40 to 26. The final precipitate powders consisted of ‘spherules’ of highly microcrystalline or amorphous polymer glass; the spherule diameters were about 0.2 μm at the critical concentrations and decreased to below 0.05 μm with increasing solution concentrations.     

Structure and self-assembly synthesis of a novel heterometallic one-dimensional coordination polymer: {[Cu(II)(DETA)I·DMF]2[Pb2I6]} n

A novel organic–inorganic hybrid coordination polymer {[Cu(II)(DETA)I·DMF]₂[Pb₂I₆]} _n (DETA = diethylene triamine, DMF = N,N′-dimethyl formamide) was synthesized by the reaction of CuSO₄·6H₂O, DETA, Pb(NO₃)₂ and NaI in DMF/H₂O mixed solvent at room temperature. Structural characterization of X-ray single diffraction reveals that the polymeric negative chain [Pb₂I₆] _n ²⁻ is built up by face-sharing of PbI₆ octahedrons. Upon the hydrogen bonds interaction between N–H···I and N–H···O, structure-directing reagent chain {[Cu(II)(DETA)I·DMF]₂} _n ²⁺ presents one-dimension arrangement. Structure-directing reagent chains and polymeric negative chains are in combination with each other by static attracting force to form the so-called hybrid structure. The title compound was further characterized by IR, EA, UV-Vis and fluorescence spectrum.     

Synthesis and Crystal Structure of Pivalamidate-Bridged Trinuclear Platinum–Copper Complex with a Linear Pt–Cu–Pt Core

Abstract The heterotrimetallic complex [Cu{trans-Pt(NH₃)₂(NHCO^tBu)₂}₂](NO₃)₂ was synthesized and structurally characterized by X-ray crystallography. The cationic complex consists two trans-[Pt(NH₃)₂(NHCO^tBu)₂] units and one Cu²⁺ ion, which are linearly held together by four bridging pivalamidate ligands. The compound crystallizes in the monoclinic space group P2₁/c with a = 13.18(1) ?, b = 13.12(1) ?, c = 21.38(2) ?, β = 116.88(3)°?, V = 3674(5) ?³, and Z = 4. The trimeric Pt–Cu–Pt cation further aggregates into a dimer of trimer via a weak Pt···Pt interaction. Graphical abstract Synthesis and crystal structure of pivalamidate-bridged trinuclear platinum–copper complex with a linear Pt–Cu–Pt core Chao Chen, Huayu Qiu*, Fenghui Liu and Wanzhi Chen* A heterotrimetallic complex [Cu{trans-Pt(NH3)₂(NHCO^tBu)₂}₂](NO₃)₂ was synthesized and structurally characterized by X-ray crystallography.      

On the stereochemistry of 7-[1(2-carbomethoxyanilino)-1-(pyridyl)-methyl]-quinolin-8-ol (CMAP-oxine)

C₂₃H₁₉N₃O₃, P1 , a = 11,683(3), b = 7.740(2), c = 14.445(3) Å, α = 131.02(8), β = 95.43(8), γ = 95.02(8)°, D_x = 1.328 Mg · m⁻³, V = 0.9614 · 10⁻²⁷ m³, Final R = 0.059 for 2905 symmetrically independent reflections (|F₀| ≧ 3σ(F₀)). The intensities were measured with an automatic diffractometer. There are two molecules in the unit cell. The substance is not tridentat in potentially coordination behaviour; coordination takes place (twodentat) on the oxine group.     

Growth,thermophysical and electrical properties of the nonlinear optical crystal BPO4

Bulk BPO₄ crystals have been successfully grown from high temperature solution of BPO₄, Li₂O, and MoO₃ in the molar ratio of 2.3:1:1.3 by the top‐seeded solution growth (TSSG) method using [101]^c orientation seeds. There are no visible scattering centers and impurity of Mo in the as‐grown BPO₄ crystals, whose optical homogeneity reaches up to 1.6×10^–5/cm. BPO₄ possesses a specific heat of 0.50–1.00 J·g^–1·K^–1 in the temperature range from 298 to 698 K and exhibits strong anisotropic thermal expansion behavior with α_a = 14.2 × 10^–6 K^–1 and α_c = ‐4.0 × 10^–7 K^–1. Moreover, the thermal conductivity coefficients are calculated to be κ_a = 62.4 W·m^–1·K^–1 and κ_c = 51.5 W·m^–1·K^–1, which are remarkably larger than those of some commonly used borates. The measured dielectric constants, ε_a and ε_c, are 4.8 and 6.1, respectively, and the ionic conductivity coefficients, σ_a = 4.3 × 10^–8 S/cm and σ_c = 9.5 × 10^–8 S/cm, are several orders of magnitude lower than that of LiB₃O₅ (LBO). (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallizaton Characteristics of the Alternating Tetrafluoroethylene-Ethylene Copolymer

The alternating tetrafluoroethylene-ethylene (TFE-E) copolymer has been studied with respect to its crystallization by using differential scanning calorimetry and optical microscopy. The value of the specific surface energy σ at the melt/crystal interface is calculated to be about 2 · 10⁻³ J/m². The nucleating activity Φ of TiO₂ particles introduced into TFE-E copolymer is estimated to be approximately 0.9. The temperature dependence of the nucleation rate and of the linear growth velocity are constructed in the whole region from the melting temperature T_m to the vitrification temperature T_g. The minimum cooling rate for the formation of a crystal-free TFE-E copolymer glass is calculated and its value amounts to 10⁴ K · min⁻¹.     

Induction periods and mechanism and kinetics of nucleation of barium tungstate crystal growth from sodium tungstate melts in platinum crucibles

Induction periods (t) and mechanism and kinetics of nucleation in barium tungstate crystallization from sodium tungstate melts in platinum crucibles were studied. A theoretical relation has been developed to express the dependence of t on the cooling rates (R_T) and the rate (R_c) of development of excess solute concentration. At any crystallization temperature the average rate-constant (k_n) for heterogeneous nucleation was related to R_c by (k_n/p)^1/(p+1) = 1/(tR_c^γ), where γ is a constant and p is the average number of particles in the critical nuclei. The critical temperature (T), critical supersaturation (S) and γ values were estimated.     

Structure and Luminescence of Eu-activated Zirconium Hydroxide and Dioxide at Relatively Low Temperatures

Luminescent materials with composition ZrO₂:0.01 Eu were prepared by co-precipitation of zirconium and europium hydroxides and subsequent thermal decomposition at relatively low temperature. A stabilization of tetragonal ZrO₂ prepared on this way is found. The structure of the prepared samples was investigated. The luminescence spectra of tetragonal and of monoclinic ZrO₂ · 0.01 Eu and of ZrO₂ · n H₂O:0.01 Eu by excitation at 254 nm and at 365 nm are presented.     

Crystal and molecular structure of 7-[1-(2-carbomethoxyanilino)-1-(phenyl)-methyl]-quinolin-8-ol(CMAB-Oxine) and comparising consideration to CMAP-Oxine

C₂₄H₂₀N₂O₃, Pbc2₁, a = 11.338(4), b = 7.786(3), c = 44.381(6) Å, D_x = 1.29 Mg · m⁻³, V = 3.82053 · 10⁻²⁷ m³. There are eight molecules in the unit cell (two molecules, A and B, in the asymmetric unit). The substitution of N (CMAP-Oxine) by CH(CMAB-Oxine) in the aldehyde participant of reactants creates differences both in intermolecular contacts and orientation phenomenons of ring planes. A high degree of selectivity of the substitution position for both compounds is given. The reactions to the synthesis of both compounds are difficult to agree upon with the characteristic feature of the Mannichreaction and corresponded more to the character of the electrophilic substitution of aromatics.     

Synthesis,Crystal Structure and Luminescent Properties of One Coordination Polymer of Copper(II) Achieved from Pyridine-3,5-dicarboxylate

Abstract  

A new Cu(II) coordination polymer [Cu(3,5-pdc)(H₂O)₄·H₂O] _n 1 (3,5-pdc=3,5-pyridinedicarboxylic acid) has been synthesized by hydrothermal method and characterized by IR, elemental analysis, TG technique and X-ray crystallography. The crystallographic data for the compound 1: monoclinic P2₁/n, a = 11.361(5) ?, b = 7.095(3) ?, c = 14.575(6) ?, β = 107.630(4)°, V = 1,119.7(8) ?³, Z = 4, Dc = 1.891 Mg/m³, F(000) = 652, R ₁ = 0.0374, wR ₂ = 0.1083. Cu(II) atom has an distorted octahedral environment with N₂O₄ donor set of Cu(1) and O₆ donor set of Cu(2), respectively. Each ligand is bound to two Cu(II) ions and each copper atom is coordinated by two ligands thereby generating a 1D zigzag chain. The 1D chain was interacted each other feathering three-dimensional supramolecular network through π···π interactions and multiform intermolecular hydrogen bonds. The luminescent properties of the title complex in the solid state were investigated.     

Growth process and optical investigations of Nd:NaGd (MoO4)2 crystals with varying content of Nd and Gd

In this paper, [NaGd_1‐xNdx](MoO₄)₂ crystals with x = 0.005–0.05 were grown by Czochralski method at 950 ℃ for 10 hours and subsequently characterized by absorption spectroscopy and fluorescence spectroscopy. The intensity parameters of Nd³⁺ were calculated by Judd‐Ofelt theory, and the relationship between the parameters and Nd³⁺ concentration was analyzed. The results show that with the increasing Nd³⁺ concentration, the oscillator strength, stimulated emission cross‐section, Ω_t and spontaneous transition probability decrease slightly, while the fluorescence lifetime decreases significantly. However, the fluorescence branching ratio is almost unchanged with the increasing Nd³⁺concentration. The [NaGd_1‐xNd_x](MoO₄)₂ crystal with (x = 0.01) possesses the highest quantum efficiency of 88.98%, a good fluorescence line‐width of 23 nm, a large value of σ_em·τ_f up to 0.55 × 10⁻²² cm²·s and a stimulated emission cross‐section up to 3.747 × 10⁻¹⁹ cm² for the transition from ⁴F_3/2 to⁴I_11/2 at 1064 nm. Test results indicate that [NaGd_1‐xNd_x](MoO₄)₂ crystals are an excellent gain media for the solid state laser system.