Crystallization-induced Changes Research Articles

Simultaneous Electrical, Electrochemical, and Optical Relaxation Measurements of Oxygen Surface Exchange Coefficients: Sr(Ti,Fe)O3-d Film Crystallization Case Study.

The oxygen surface exchange coefficient (k) dictates the efficiency and response time of many mixed conductors, so its accurate, continuous measurement in realistic conditions, enabling rational tailoring, is necessary. However, recent results showed that k values determined by a thin-film optical transmission relaxation (OTR) method were orders of magnitude lower than those extracted from the cross-cell AC-impedance spectroscopy (AC-IS) approach, and similar discrepancies among methods exist in the literature. OTR has also detected dramatic increases in k in situ during crystallization. Therefore, in this work, we sought to establish whether k values from OTR are reliable, and to gain further insight into crystallization-induced changes, via comparison to the electrical conductivity relaxation (ECR) method. We performed simultaneous OTR and ECR measurements on the same region of an as-grown amorphous SrTi0.65Fe0.35O2.825+δ (STF) film, prepared by pulsed laser deposition and characterized by Rutherford backscattering spectrometry, during thermal treatment to induce crystallization and a large increase in k. We also compared cross-cell AC-IS vs OTR on an as-grown amorphous film during crystallization and OTR vs ECR on a crystalline-grown film. Simultaneous measurements eliminate variability in k between samples or due to different thermal/gas history. OTR and ECR methods yielded the same k values, and the same crystallization temperature, within error. Both isothermal optical absorption and electrical conductivity changes are proportional to the hole and oxygen concentration changes under the conditions of this study. However, while OTR was able to measure optical absorption changes under all of the conditions tested, ECR was not viable in the high-resistance regime. Cross-cell AC-IS k values were elevated vs OTR values, were less stable over time, and were only accessible in limited conditions. We discuss the potential impacts of current collectors and oxygen exchange driving force on k values determined by cross-cell AC-IS vs ECR vs OTR.

Extracting the temperature distribution on a phase-change memory cell during crystallization

Phase-change memory (PCM) devices are enabled by amorphization- and crystallization-induced changes in the devices' electrical resistances. Amorphization is achieved by melting and quenching the active volume using short duration electrical pulses (∼ns). The crystallization (set) pulse duration, however, is much longer and depends on the cell temperature reached during the pulse. Hence, the temperature-dependent crystallization process of the phase-change materials at the device level has to be well characterized to achieve fast PCM operations. A main challenge is determining the cell temperature during crystallization. Here, we report extraction of the temperature distribution on a lateral PCM cell during a set pulse using measured voltage-current characteristics and thermal modelling. The effect of the thermal properties of materials on the extracted cell temperature is also studied, and a better cell design is proposed for more accurate temperature extraction. The demonstrated study provides promising results for characterization of the temperature-dependent crystallization process within a cell.

Universal relationship between crystallization-induced changes of the shear modulus and heat release in metallic glasses

It is widely known that crystallization of metallic glasses is accompanied by a strong heat release. Current literature considers this phenomenon in a general sense as a result of structural ordering and related decrease of the excess enthalpy. The only specific interpretation for the crystallization-induced heat release was recently suggested on the basis of the Interstitialcy theory and elastic dipole model. This work presents measurements of the heat release and changes of the shear modulus taking place upon crystallization of a series of Zr- and Pd-based metallic glasses. The analysis of the performed experiment provides further clear support for the interpretation of the heat release as a result of the disappearance of interstitialcy-like ”defects” (elastic dipoles) frozen-in from the melt upon glass production and related dissipation of their elastic energy. Analytically, the heat release is controlled by the change of the shear modulus upon crystallization constituting thus a universal relationship between these quantities.

The effect of phase separation on subsequent crystallization in Al 88Gd 6La 2Ni 4

To understand the crystallization (devitrification) kinetics of Al-rich Al–RE–TM (RE=rare earth, TM=transition metal) amorphous alloys, the devitrification of Al 88Gd 6La 2Ni 4 was studied by in situ electrical resistivity and transmission electron microscopy (TEM) investigations. This glass composition was chosen because it shows a well-defined glass transition temperature ( T g) and transforms to α-Al on partial devitrification. Surprisingly, we show that crystallization appears to be preceded by a phase separation into Al-rich and solute-rich amorphous regions, having a typical dimension of 40 nm. TEM studies reveal a preferential rapid nucleation of α-Al at the interface of the phase-separated regions. A Johnson–Mehl–Avrami analysis of crystallization-induced changes in the electrical resistivity shows limited agreement with the theory, with an Avrami exponent n close to unity. This is explained by a simple numerical model that is consistent with the microstructure; i.e., rapid nucleation at the phase boundary followed by diffusion-limited growth.

Influence of microstructure on magnetic and mechanical behavior in amorphous and nanocrystalline Fe 73.5Nb 4.5Cr 5Cu 1B 16 alloy

The amorphous Fe 73.5Nb 4.5Cr 5Cu 1B 16 alloy is transformed to two-phase nanocrystalline material in the temperature range 450–550 °C. The changes in microstructure upon annealing are examined by X-ray diffraction and transmission electron microscopy. The resulting structure is composed of b.c.c.-Fe nanocrystalline grains with diameter of about 4–8 nm embedded in residual amorphous matrix. The correlations between microstructure and magnetic and mechanical properties in a series of heat treated amorphous and nanocrystalline samples are studied by VSM-magnetometry, hysteresis loop measurements and bending tests. It is shown that all obtained magnetic parameters depend strongly on a degree of crystallization in the investigated alloys. The degradation of soft magnetic properties with an increasing fraction of the nanocrystalline phase is supposed to be a consequence of the crystallization-induced changes in the residual amorphous matrix, which results in the weakening of the exchange coupling between nanocrystalline grains. The results of bending tests show that an embrittlement in investigated alloy occurs predominantly in the temperature region 200–400 °C, i.e., before nanocrystallization, being probably related to the atomic rearrangements in amorphous phase.

Fassaite composition trends during crystallization of Allende Type B refractory inclusion melts

Fassaite is a major phase in Type B refractory inclusions and its wide compositional variability makes it an excellent recorder of crystallization-induced changes in liquid composition. Traverses across zoned crystals with electron and ion microprobes show that Ti, V, Sc, Zr and Hf decrease from core to rim, while Mg, Si, REEs, and other trace elements increase. Fassaite/liquid distribution coefficients derived from the compositions of early fassaite and calculated parent liquid compositions are higher than previously reported fassaite Ds, e.g., 0.2–0.8 vs. 0.08–0.5 for the trivalent REEs, possibly due to the high Ti and Al contents of the fassaite we analyzed. Log-log plots of concentrations of elements vs. those of Sc give linear relationships with slopes of (D̄ixl/L − 1)/(D̄Scxl/L − 1), where D̄ixl/L- is the bulk crystal/liquid distribution coefficient for element i. From this relationship, we derive effective fassaite/liquid Ds of 2.8 for Sc, 1.5 for Hf, 1.1 for Zr, 0.52 for Y, 0.34 for Ta, 0.29 for Nb, and 0.31–0.48 for trivalent REEs. The effective Ds are applicable to fassaite crystallizing from melts having the compositions and thermal histories of Allende Type B refractory inclusions, and incorporate any equilibrium and kinetic effects that modify Ds during the course of crystallization. Observed fassaite REE contents can be reproduced by a fractional crystallization model in which the effective Ds are used. Ti3+ is more compatible in fassaite than Ti4+ and, without equilibration of the residual liquid with an external reducing gas, Ti3+Titot ratios (where Titot = Ti3+ + Ti4+ should decrease from core to rim in fassaite crystals. Comparison of profiles of Ti3+Titot ratios in several crystals with those calculated for fractional crystallization suggests that the trend in one crystal was controlled by fractional crystallization alone, but in two others the virtually constant Ti3+Titot ratios may imply that the liquids in these inclusions were able to maintain equilibrium with the solar nebular gas throughout crystallization. Attempts to determine the ƒo2 of fassaite crystallization on the basis of Ti3+Titot ratios must be based on fassaite grains which are not zoned with respect to Ti3+Titot. The range of observed REE abundances in subliquidus fassaite (7–800 × Cl for La and 30–2000 × Cl for Lu) now encompasses those in grains previously identified as relict, removing a major reason for their identification as such. Rounded fassaite grains with fairly sharp Mg-rich rims and Ti-rich cores, poikilitically enclosed in mantle melilite in TS34 are candidates for relict grains. The grains are so Scrich that they would require extreme prior crystallization of spinel and melilite, which is inconsistent with their very low REE contents (e.g., La at 3–7 × Cl). We suggest that the cores of these grains are relict and were trapped with liquid during formation of the mantle.

ChemInform Abstract: CRYSTALLIZATION‐INDUCED CHANGES IN PROTEIN STRUCTURE OBSERVED BY INFRARED SPECTROSCOPY OF CARBON MONOXIDE LIGANDED TO HUMAN HEMOGLOBINS A AND ZURICH

Chemischer InformationsdienstVolume 16, Issue 38 Physical Organic Chemistry ChemInform Abstract: CRYSTALLIZATION-INDUCED CHANGES IN PROTEIN STRUCTURE OBSERVED BY INFRARED SPECTROSCOPY OF CARBON MONOXIDE LIGANDED TO HUMAN HEMOGLOBINS A AND ZURICH W. T. POTTER, Search for more papers by this authorR. A. HOUTCHENS, Search for more papers by this authorW. S. CAUGHEY, Search for more papers by this author W. T. POTTER, Search for more papers by this authorR. A. HOUTCHENS, Search for more papers by this authorW. S. CAUGHEY, Search for more papers by this author First published: September 24, 1985 https://doi.org/10.1002/chin.198538065AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume16, Issue38September 24, 1985 RelatedInformation

Crystallization-induced changes in protein structure observed by infrared spectroscopy of carbon monoxide liganded to human hemoglobins A and Zurich

Crystallization-induced changes in protein structure observed by infrared spectroscopy of carbon monoxide liganded to human hemoglobins A and Zurich