Crystallization kinetics of lithium niobate films from limited volume of melt solution

The growth kinetics of LiNbO₃ films from a limited volume of melt solution is observed. We developed crystallization models describing the character of mass transfer in the liquid phase for isothermal and non-isothermal epitaxy. Analytical expressions have been derived connecting the film thickness with the system growth parameters. The experimental values being in good agreement with the calculated ones.     

Field-driven redistribution of “guest protons” within protonated silicate glasses

Protonated layers of lithium silicate glasses generated by electrolysis were penetrated by lithium ions from appropriate anodic solutions during a second electrolysis. As the electric fields were applied in the same direction during both electrolyses, the number of protons within the glasses was unchanged. As is made apparent in the discussions of the local resistivities and the resulting profiles of the electric fields within the electrolysed membranes, the steady state of the protonated layer was disturbed by the lithium ions making the migrating front of the less mobile protons unstable. The protons were diluted, while simultaneously the layer thickness was increased.

A remarkable change in the ir spectrum observed after the second electrolysis and indicating that Beer's law is not valid is explained by the tendency of protons to occupy preferred sites. It is proposed that mixed twin siloxy groups containing one lithium ion and one proton with different bond energies and thus different probabilities for leaving the entity act as proton traps and function as single sites for migrating lithium ions. The effect was observed with several lithium silicate glasses but not with a lithium aluminum silicate glass. Protons introduced as probes for alkali into glasses may thus contribute information on the glass structure.     

Improved Single Crystal Growth of the Boron Sillenite “Bi24B2O39” and Investigation of the Crystal Structure

The boron sillenite, up to now known as the 12:1 compound Bi₂₄B₂O₃₉ in the system Bi₂O₃ – B₂O₃ andcrystallizing in the space group I23, melts incongruently at 655 °C only about 25 K above the eutectic tie line and corresponding to a steep liquidus line. Single crystals with dimensions larger then 1 cm ³ have been successfully grown in [100], [110], and [111] direction by an improved Top Seeded Solution Growth (TSSG) technique equipped with crucible weighing, accelerated crystal rotation technique and air‐cooled pulling rod. The structure of the boron sillenite was analyzed by X‐ray diffraction method, which was possible due to the high crystalline quality achieved. A defect‐free sublattice corresponding to a Bi‐O framework is isostructural with all sillenites, but a 2 Å environment around the origin is occupied by different cations with different population coefficients. The best calculation results in the formula Bi_24.5BO_38.25 which is more Bi‐rich than the 12:1 assumption.     

KOWARSKI “Protuberances” as an Example of Two-Dimensional Growth by the VLS Mechanism

The growth kinetics of protuberances formed in the presence of water vapour at the surface of paratoluidine crystals growing from the melt was investigated. The experimental quadratic dependence of the flux of matter directed towards the droplet on its radius leads to the view that KOWARSKI 's protuberances constitute an example of crystal growth by the VLS mechanism.     

Instability of “slow” solid-liquid interface relaxation before the hetero-LPE of III-V compounds

Results of specially designed experiments supplemented by numerous literature examples have been analysed in attempt to elucidate the processes occurring at the interface between saturated multicomponent liquid and a non-equilibrium solid before the hetero-LPE of nearly lattice-matched III–V compounds. The “slow” interface relaxation which provides the moving of non-equilibrium solid-liquid system in the direction of thermodynamic equilibrium by solid-state diffusion (and which was previously believed to be the only way of equilibrium approach in lattice-matched systems) looses the stability in some cases, being replaced by “fast” relaxation. It has been shown that the liquid-solid interface instability develops due to a collective action of several factors, and their particular combination produces definite mode of relaxation. The “slow” relaxation would be unstable, if, as a result of underlying solid dissolution: (1) the lattice parameter of equilibrium solid decreases continuously with respect to that of the substrate, increasing thereby the driving force for dissolution; (II) the solubility of group V component in a changed liquid increases. In a majority of cases the switching to “fast” relaxation is facilitated by (III) the initial negative difference between the lattice parameters of equilibrium and underlying solids at the growth temperature.     

Ba2.2Ca0.8Mg4F14, a new “solid solution stabilized” matrix for an intense blue phosphor

Barium calcium magnesium fluoride (Ba₂(Ba_xCa_1‐x)Mg₄F₁₄, x=0.19‐0.26) has been synthesized at 850 °C from precursors prepared by the solution precipitation method. Single crystals with composition of Ba_2.200(2)Ca_0.800(2)Mg₄F₁₄were obtained after prolonged heating. Lattice parameters from single crystal data are a = 12.4203(8) and c = 7.4365(5) Å [tetragonal, space group P4₂/mnm (No. 136)]. They increase with increasing barium concentration within a given stability window. The structure is built of a network of MgF₆ octahedra forming a pyrochlore related channel system and isolated fluorine ions. Within the channels, heavy alkaline earth ions are located. The wide channel is filled with off‐center positioned barium ions. The channel with a narrow cross section hosts both ions, Ca²⁺and Ba²⁺. The structure is isotypic with Pb₃Nb₄O₁₂F₂ but has a different coordination around Ba/Ca and Pb, respectively. Doped with ∼1% Eu(II), the compound shows intense blue luminescence under UV activation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

“Amorphous” Precursors of α-Al2O3: An Electron Optical Study

Basic aluminium chloride gels are thermally decomposed into X-ray amorphous products. Corundum begins to crystallize in them about 400 °C on certain conditions. Electron optical examinations on powders of corundum-forming gels and of their decomposition products show in an essential part aggregates of sheetlike components as powder particles. These have sharp electron diffraction patterns. The interpretation of diagrams proves the existence of two different structures with similar lattices, which are evidently related to those of diaspore and corundum. A defect structure is to be assumed for the corundum crystals formed.     

Growth of KDP crystals by splicing “parallel”-seed in aqueous solution and its mechanism

Growth of the habit of a single seed and the special growth of splicing “parallel” seeds were investigated and compared with. Chemical etching and X-ray topography were used to characterize spliced KDP crystals. The kinetic data in different growth stages were measured. It is concluded that secondary capping is the most important stage in the splicing parallel-seed growth, and that the subgrain boundaries emitted from the secondary cap are parallel to or overlap with the splicing boundary and stretch to the prismatic surface about 45° to the z-axis, and that above the twin-crystal regions with subgrain boundaries the real monocrystalline region appears. The growth kinetics of the subgrain boundary approximately corresponds to the growth mechanism of single-spiral dislocation.     

Thermoanalytical Investigations to Understand the Dependence Between the Growth Method and Crystal Properties of Valence Changing “YbInCu4”

The solidification phase diagram for the system Yb–In–Cu is investigated in the neighbourhood of the valence changing composition YbInCu₄ by means of differential thermal analysis. It is found that the solid phase with the structure of YbInCu₄ exists within a finite composition range and that the congruent melting composition of this phase is shifted towards Yb-rich composition with respect to the stochiometric composition. Temperature dependent x-ray powder diffraction is used to detect the valence transition of the “YbInCu₄-phase”. This transition occurs at appr. 40 K for samples grown from melts with an Yb-content less than 0.7 with respect to the formula Yb_xIn_2—xCu₄ while a higher Yb-content leads to a transition temperature of about 70 K. This is seen as a consequence of a change between differently ordered structures that occurs at a certain Yb-content.     

”︁Four-fold„ refringence in quartz

An attempt is made to interprete the simultaneous existence of four refractive indexes (two ordinary and two extraordinary) near the α—β phase transition in quartz from the optical point of view. The theory of thermodynamical stability predicts the appearance of fluctuation areas of the α- and β-phases in the vicinity of the α—β transition. On the basis of this theory the formation of infinite clusters, consisting of the merged fluctuation ranges, is assumed.     

Reply to “Comments on papers reporting IR‐spectra and other data of L‐alanine alaninium nitrate and L‐alanine sodium nitrate crystals” by M. Fleck and A. M. Petrosyan

The formation of the new compounds of L‐alanine alaninium nitrate and L‐alanine sodium nitrate has been presented with adequate explanation with the aid of the FTIR, XRD and NLO measurements as a reply to “Comments on papers reporting IR‐spectra and other data of alleged L‐Alanine Alaninium Nitrate and L‐Alanine sodium nitrate crystals by M. Fleck and A.M. Petrosyan” (Cryst. Res. Technol. 44 , 769, 2009). The variation in the lattice parameters, physical properties, chemical properties and nonlinear optical behaviour from the L‐alanine ensures the formation of the new compounds L‐alanine alaninium nitrate and L‐alanine sodium nitrate. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comment on the paper “Contribution to the stability analysis of the dewetted Bridgman growth under microgravity conditions”

New considerations of the stability problem of dewetting, as addressed in the initial paper [Cryst. Res. Technol. 39 , 491 (2004)], show that, in the most general case, when dewetting occurs in microgravity it is necessarily stable. This explains why the phenomenon has been observed so many times during solidification of semiconductors in space. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comment on “the growth of dicalcium phosphate dihydrate on octacalcium phosphate at 25°C” by J.-C. Heughebaert, J.F. De Rooij and G.H. Nancollas

An apparent disagreement with respect to the growth kinetics of octacalcium phosphate (OCP) is shown to arise from different methods of data analysis.     

Investigation of the cluster formation in lithium niobate crystals by computer modeling method

The processes occurring upon the formation of energetically equilibrium oxygen-octahedral clusters in the ferroelectric phase of a stoichiometric lithium niobate (LiNbO₃) crystal have been investigated by the computer modeling method within the semiclassical atomistic model. An energetically favorable cluster size (at which a structure similar to that of a congruent crystal is organized) is shown to exist. A stoichiometric cluster cannot exist because of the electroneutrality loss. The most energetically favorable cluster is that with a Li/Nb ratio of about 0.945, a value close to the lithium-to-niobium ratio for a congruent crystal.