Manipulating the Mixed‐Perovskite Crystallization Pathway Unveiled by In Situ GIWAXS

Mixed perovskites have achieved substantial successes in boosting solar cell efficiency, but the complicated perovskite crystal formation pathway remains mysterious. Here, the detailed crystallization process of mixed perovskites (FA_0.83MA_0.17Pb(I_0.83Br_0.17)₃) during spin‐coating is revealed by in situ grazing‐incidence wide‐angle X‐ray scattering measurements, and three phase‐formation stages are identified: I) precursor solution; II) hexagonal δ‐phase (2H); and III) complex phases including hexagonal polytypes (4H, 6H), MAI–PbI₂–DMSO intermediate phases, and perovskite α‐phase. The correlated device performance and ex situ characterizations suggest the existence of an “annealing window” covering the duration of stage II. The spin‐coated film should be annealed within the annealing window to avoid the formation of hexagonal polytypes during the perovskite crystallization process, thus achieving a good device performance. Remarkably, the crystallization pathway can be manipulated by incorporating Cs⁺ ions in mixed perovskites. Combined with density functional theory calculations, the perovskite system with sufficient Cs⁺ will bypass the formation of secondary phases in stage III by promoting the formation of α‐phase both kinetically and thermodynamically, thereby significantly extending the annealing window. This study provides underlying reasons of the time sensitivity of fabricating mixed‐perovskite devices and insightful guidelines for manipulating the perovskite crystallization pathways toward higher performance.     

Electron-microscopic study of glassy As2Te3

Electron-microscopic investigations of glassy As₂Te₃ reveal that this material is a homogeneous glass and does not contain any crystalline phase. In order to verify the detection limit of the employed method with respect to crystalline phase the presence of the latter was provoked by heating the glass in DTA. The crystallization procceeds in two stages: (1) in T_g region the growth of crystallization centres originating probably from the initial melt starts; (2) closely below the recrystallization temperature T_r spontaneous crystallization in the whole glassy bulk is initiated.     

Crystallization and thermally induced surface relief effects in a Mg<Subscript>65</Subscript>Cu<Subscript>25</Subscript>Y<Subscript>10</Subscript> bulk metallic glass

The crystallization behaviour of Mg₆₅Cu₂₅Y₁₀ bulk metallic glass (BMG) under different reheating conditions was investigated. X-ray diffraction spectrometery (XRD), differential scanning calorimetery (DSC), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to examine the crystallization of different samples and the surface relief generated on as-polished surfaces during heat treatment. Different phase constituents were found in samples that experienced different reheating stages. It is proposed that both the reheating temperature and holding time have a significant effect on the phase constituents. The BMG was found to generate surface corrugations of amplitude 1–2 μm during annealing above its crystallization temperature. Such thermally induced surface relief effects are probably a result of the development of surface stresses generated by volumetric changes associated with crystallization of the residual amorphous phase.     

Crystallization characteristics of amorphous Fe-Si-B alloys

Crystallization of soft magnetic Fe-Si-B glasses was investigated by transmission electron microscopy and X-ray diffraction. Electron micrographs of the successive crystallization stages of some Fe-Si-B glasses were obtained and the morphology variations for different alloy compositions were determined. The compositional dependence of the crystallization mode exhibited by the Fe-Si-B glasses was analysed, and on this basis some suggestions about crystallization rules in these glasses are proposed. Two kinds of iron—silicon phases occurred, depending on the Fe-Si-B alloy composition: bcc Fe(Si) solid solution and an ordered solid solution on the structural basis of Fe₃Si iron suicide. It is suggested that the metastable Fe₃B phase (observed during crystallization of only few glasses) was not a simple consequence of boron content. Crystallization of the Fe₃B phase was related to the formation of the iron—silicon phase which was produced during the first crystallization stage.     

Crystallization of amorphous Ni60 Nb40−x Cr x alloys

Crystallization behaviour of amorphous Ni₆₀ Nb_40-x Cr _x (x = 0, 5, 10 and 13 at%) alloys was studied by differential Scanning calorimetry and X-ray diffraction measurements. It is shown that the addition of chromium reduces the crystallization temperature, stages of crystallization and activation energies associated with the crystallization sages of the Ni₆₀Nb₄₀ glass. Crystallization of the Ni₆₀Nb₄₀ glass occurred in three stages; in the initial stage a metastable M-phase formed in the amorphous matrix as reported earlier [1] . However, contrary to earlier observation [1], M -phase was not very stable and transformed together with some amorphous phase to the equilibrium Ni₃Nb phase in the second stage of crystallization. In the third stage, the remaining amorphous matrix transformed to the equilibrium NiNb phase. On addition of chromium the formation/stability of the M-phase was found to be suppressed and equilibrium NbCr₂ phase precipitated preferentially in the first stage. The second stage, corresponding to the formation of Ni₃Nb phase, remained almost unaltered. The third stage corresponding to the crystallization of NiNb phase disappeared completely at 13 at% Cr. In the fully crystallized samples the proportion of the NiNb phase decreased and that of NbCr₂ phase increased continuously with chromium concentration.     

Two-stage crystallization kinetics equation and nonisothermal crystallization analyses for PTEG and filled PTEG

A novel modified Avrami model considering both primary and secondary crystallization has been presented to extract the kinetic behavior of these two crystallization stages in nonisothermal crystallization process of polymers. Nonisothermal crystallization kinetics of poly(trimethylene terephthalate)–poly(ethylene glycol) segmented copolyesters (PTEG) has been investigated by differential scanning calorimetry. The crystallization rate constants and Avrami exponents at various cooling rates were obtained from the analyses for neat PTEG and multiwalled carbon nanotube (MWNT) filled PTEG. Secondary crystallization displays a lower-dimensional crystal growth compared with primary crystallization and the results of kinetics analyses are consistent with morphology study. The MWNTs introduced into PTEG matrix take the role of effective nucleating agents during composites crystallization and can expedite the process of crystallization of the matrix by providing more nucleation sites to the crystallizing phase.     

Measuring strain changes during production of thin film crystalline silicon on glass photovoltaic modules

We report on strain measurements made on samples of thin-film crystalline silicon on borosilicate glass solar cell obtained from CSG Solar after two significant thermal stages of production. Samples were obtained both after solid phase crystallization and subsequent rapid thermal annealing of the silicon. Results indicate a large change in strain between stages. After solid phase crystallization the polysilicon was found to be in a state of high compressive residual strain with an average recorded value of −0.24%. After the subsequent annealing this film strain present in the polysilicon was almost entirely passivated, reducing by a factor of 4.7 to record an average strain post annealing of −0.051%.     

Atomistic simulations of spinodal phase separation preceding polymer crystallization

Many polymeric materials crystallize when cooled below their melting temperature. Although progress has been made in our understanding of the crystallization process through both experimental and theoretical efforts, these studies have focused mainly on the crystal nucleation and growth mechanism, where critical nuclei are formed from a metastable state during the first stages of crystallization, leading ultimately to the growth of crystal domains. Attention has also been given to the structure during the precrystallization (induction period). A pretransition state occurring before crystallization has been characterized as an unstable phase separation initiated by density and orientational fluctuations. These fluctuations are caused by an increase in the average length of rigid trans segments along the polymer backbone during the induction period. These observations are consistent with the theory proposed in ref. 14 on the isotropic-to-nematic transition of polymer liquid crystals, that is, the parallel ordering of polymers is caused by an increase in chain rigidity. Here we use large-scale computer simulations to investigate melts of polymers in the early ordering stages (induction period) before crystallization. In the ordered domains we identify growing dense regions similar to smectic liquid crystals. Our simulations reveal a 'coexistence period' in the ordering before crystallization, where nucleation and growth mechanisms coexist with a phase-separation mechanism.     

纯化—反应—浓缩—结晶—分级工序合一的液膜工艺(Ⅰ)

首次提出了一个对某些化工过程可将五个工序合而为一的液膜工艺,对合并的可能性进行了理论分析和六个可行性的试验,对从中选出的一个在合并难度上具有代表性的仲钨酸铵结晶的生产所作全面性的试验,技术上和经济上结果都十分成功,在此基础上,提出了用此工艺日产100公斤APT的技术方案和经济预测。     

Shape of grain size distributions during crystal grain nucleation in a-Si

The solid phase crystallization of chemical vapor deposited amorphous silicon films onto oxidized silicon wafers, induced by rapid thermal annealing has been extensively investigated. The morphological evolution of the amorphous towards the polycrystalline phase is investigated by transmission electron microscopy and it is interpreted in terms of a physical model containing few free parameters related to the thermodynamical properties of amorphous silicon and to the kinetic mechanisms of crystal grain growth at the early stages of transformation.     

On the crystallization of Fe77B16Si5Cr2 alloy

The crystallization of the Fe₇₇B₁₆Si₅Cr₂ alloy is characterized by calorimetric (DSC) and X-ray diffraction experiments. Two crystallization stages are resolved in DSC records with ΔH₁ = 3.6 ± 0.1 and ΔH₂ = 3.1 ± 0.1 kJ/mol and kinetics of the two exotherms is derived from isothermal annealing experiments in the Johnson-Mehl-Avrami approach. The precipitation of α-Fe and σ-FeCr phases in the first stage is followed by polymorphic crystallization of α-Fe and Fe₂B phases in the second stage in which the σ-FeCr phase is also transformed into α-Fe phase.     

钠镁铝硅系统微晶玻璃的分相成核行为

本文以20Na2O、4CaO、12MgO、22Al2O3、4TiO2、38SiO2(重量百分比)组成玻璃为基础,制备了具有快速微晶化特性的钠镁铝硅系统微晶玻璃。分别采用差热分析技术(DTA)、X射线衍射技术(XRD)研究了不同热处理条件下玻璃分相成核的动力学、热力学和它们之间的依存关系。玻璃分相成核最大速率时的温度接近于923K。在成核温度的热处理对分相的放热行为有影响,成核导致系统自由能的降低与分相峰面积和峰值温度变化有关。用差热分析仪测量的玻璃分相的放热效应,是快速微晶化玻璃的重要特征,用XRD证实分相放热过程中没有微晶相产生。玻璃的分相过程为成核生长机理,采用修正kissinger方程求得玻璃分相活化能为310.445KJ/mol。     

Crystallization of (Fe, Co)78Si9B13 alloys: influence of relaxation processes

Crystallization of Fe78-xCoxSi9B13 amorphous alloys has been studied by differential scanning calorimetry (DSC), thermomagnetic gravimetry and X-ray diffraction techniques. Thermal stability of the amorphous alloy monotonically decreases with increasing cobalt content. The devitrification process as detected by DSC occurs in two main stages partially overlapping in temperature, but magnetic characterization reveals a third stage for cobalt-rich alloys. Primary precipitation of -(Fe, Co) is followed by a polymorphic reaction to give (Fe, Co)2B phase. Fe3B-type phase is also detected at the end of the first crystallization stage for iron-rich alloys and -Co(Si) and Co2B phases are found in fully crystallized samples for x=60. The influence of relaxation processes on the crystallization was investigated, but no significant effects of pre-annealing on the crystallization parameters resulted. © 1998 Chapman & Hall     

The thermal stability of Ni-11 wt% P metallic glass

A study of the crystallization of the metallic glass Ni₈₁P₁₉ was undertaken. A portion of the crystallization time-temperature-transformation curve was determined and compared with curves published by other authors. The composition and structure of the as-received metallic glass was determined. Crystallization kinetics of the glass and activation energy data were determined. Crystallization of the glass involved nucleation and growth of the crystalline phase from both the surface of quenched-in crystals and the bulk of the material. The activation energies obtained were similar for incubation, nucleation and growth. This along with supporting experimental evidence suggests that there is no activation barrier to nucleation and that all stages of crystallization are controlled by diffusion.     

TiO2 anatase thin films deposited by spray pyrolysis of an aerosol of titanium diisopropoxide

Titanium dioxide thin films were deposited on crystalline silicon (100) and fused quartz substrates by spray pyrolysis (SP) of an aerosol, generated ultrasonically, of titanium diisopropoxide. The evolution of the crystallization, studied by X-ray diffraction (XRD), atomic force (AFM) and scanning electron microscopy (SEM), reflection and transmission spectroscopies, shows that the deposition process is nearly close to the classical chemical vapor deposition (CVD) technique, producing films with smooth surface and good crystalline properties. At deposition temperatures below 400 °C, the films grow in amorphous phase with a flat surface (roughness∼0.5 nm); while for equal or higher values to this temperature, the films develop a crystalline phase corresponding to the TiO₂ anatase phase and the surface roughness is increased. After annealing at 750 °C, the samples deposited on Si show a transition to the rutile phase oriented in (111) direction, while for those films deposited on fused quartz no phase transition is observed.     

Crystallization kinetics of zeolite ZSM-5

Zeolite ZSM-5 was synthesized from aluminosilicate gels in the presence of organic templates — tetrapropylammonium bromide (TPABr) and pyrrolidine (Py) — at temperatures of 423, 438 and 453 K. Nucleation and crystallization processes were subjected to a detailed kinetic analysis. The nucleation region is subdivided into two periods: induction and transition ones. Values of nucleation energy and crystallization energy, preexponential factor, rate of crystallization, and geometric factor have been calculated. Correlations between the estimated kinetic characteristics were found. The activation energy and the preexponential factor for the transitional and crystal-growth periods have the character of a kinetic compensation effect. The mechanism of the crystallization process is discussed on the basis of the kinetic features and correlations.     

Crystallization Characteristics of YBa2Cu3O7?δ Film during TFA-MOD

The phase formation and film shrinkage during the crystallization process of YBa₂Cu₃O_7−δ (YBCO) film prepared by the trifluoroacetate organic deposition (TFA-MOD) were investigated through a series of quenching experiments. X-ray diffraction patterns show that the YBCO grains initially form following the formation of the Ba-O-F phase at the heating ramp between 720 °C and 770 °C in the case of a high heating rate of 20 °C/min. It is identified that the crystallization process is involved three stages, i.e., the first one characterized by the formation of the Ba-O-F phase, the second one by the YBCO grain nucleation together with the significant shrinkage of films, and the last one by continuous YBCO grain growth. Moreover, a heterogeneous Cl element is believed to arise from the flowing water vapor, and it may move into the intermediate pyrolyzed film. It is observed that the densification process existing in the secondary stage can be destroyed by the exterior Cl element, leading to a more porous structure in contrast to their surrounding.     

Kinetics of crystallization of a Fe74Co10B16 glass

Differential scanning calorimetry (DSC) technique has been employed to study the crystallization kinetics of a Fe₇₄Co₁₀B₁₆ glass. Crystallization of Fe₇₄Co₁₀B₁₆ glass is known to occur in two distinct stages. It was possible to separate out the isothermal kinetics of both the crystallization stages through a thermal treatment scheme in the DSC. The crystallization processes are interpreted in the light of the kinetic data obtained.     

The effect of aluminium on mechanical properties and thermal stability of (Fe,Co, Ni)-Al-B ternary amorphous alloys

Amorphous phase formation has been found in a wide range of Fe-Al-B, Co-Al-B and Ni-Al-B ternary systems by a melt-quenching technique. The aluminium content of these amorphous alloys is in the range 0 to 60 at % for Fe- and Co-Al-B systems and 0 to 26 at % for the Ni-Al-B system, but the formation of ductile amorphous phase is limited to less than 20 at % Al. Crystallization temperature and Vickers hardness increase with increasing aluminium and boron content and maximum values are attained at 887 K and 880 diamond pyramid number (DPN). Their fracture strengths are about 2140 to 2680 MPa. The effectiveness of aluminium on the increase in crystallization temperature and hardness is greater in the case of other metal elements such as chromium, manganese, iron, cobalt and nickel, but is less than the metalloid elements such as silicon and boron. This could be reasonably explained by the assumption that aluminium may also possess a weak metalloid character.