Phase meta-stable

In the case of lithium orthoniobate, Li3Nb04, no meta-stable phase was found that had a rock-salt crystal structure with disordered cation distribution [268]. Nevertheless, solid solutions Li2+xTii-4xNb3x03, where 0 < x < 0.22, have a monoclinic structure at low temperatures and undergo transformation to a disordered NaCl type structure at high temperatures [274]. 

Transfomation from a meta-stable phase, such as supersaturated solution, to a thermodynamically more favorable phase requires first the crystal nucleation of a germ of the new phase. According to the classical nucleation theory, the volume nucleation rate J (cm" sec ), describing the number of nuclei(i.e., a critical germ) formed per volume per time, is given by ... 

Compute Tnuci.j for i M tn+i) according to the classical nucle-ation theory Tnud,i = l/(Jnud,il (tn+i)), update the expected crystallization time fcryst,i tn+i) for the meta-stable phases M (t +i)... 

Keywords Alkoxy alanes in CVD Siloxy alanes in CVD Meta-stable phases Nanocomposites Mechanisms in CVD... 

Another important outcome of these CVD experiments is the possibility to synthesize meta-stable phases as transparent films, like HAIO. The subsequent local treatment with different energy beams allows the structural patterning of the meta-stable layers to create chemical landscapes, which have the characteristics to consist of physically and chemically different regions of the surface (A1 AI2O3 parts in a HAIO matrix). These patterns can in principal be reduced to nanometer scales, opening a large field of applications. 

Recently, the synthesis of truly triple and quadraple perovskites has been reported in the literature by way of metathesis reactions. The low temperatures routes are necessary to realize the formation of otherwise meta-stable phases. Articles describing the utility of topotactic methods for the synthesis of several perovskite and related phases can be found elsewhere. ... 

CHEMICAL PROPERTIES stable from 870-914C (1598-1677 F) at atmospheric pressure persists as a meta-stable phase below 8°C (46.4°F) forms low tridymite below 1 °C (34°F) and middle tridymite from 117-1°C (242.6-34°F) dissolved by hydrofluoric acid, forming the gas silicon tetrafluoride slowly attacked by heating with concentrated phosphoric acid rarely attacked by alkalies FP (NA) LFL/UFL (NA) AT (NA) HC (NA) HF (-910.7 kJ/mol crystal at25°C) Hf(8.51 kJ/mol at 1883K). 

The first interpretation of this newly identified short-time breakup of thin nematic films was put forward by van Effenterre et al. [73] and is rooted in basic thermodjmamics, i.e., in the biphase coexistence of the two (meta)stable phases taking part in the discontinuous transition. However, as pointed out in detail by Ziherl and Zumer [74], the explanation misses two critical points First, that the isotropic-nematic coexistence can only exist in the temperature range where both phases are thermodynamically metastable or stable, and second, that the nematic director is only distorted in thick enough films (i.e., above the critical thickness dc = [Ai — A2I). Therefore, the dewetting process in thin LC films is still an open question for both theoretical and experimental studies. 

A schematic representation of the thermodynamic stability lines of the two phases are reported in the left-hand side of Figure 9.10 as a function of the reciprocal lamellae thickness. At any value of the lamellae thickness, the stable phase is presented as a solid line, whereas the meta-stable phase is presented with a broken line. The intersection of the phase lines defines a triple point Q, where all three phases (the melt, the a, and the P crystals) can coexist as stable phases. From the viewpoint of kinetics, the smaller the critical nucleus, the faster the crystallization rate of crystalline phase. The crystallization rate of the a form is thus expected to be faster than that of the p form in the temperature range approaching the glass temperature and vice versa close... 

The predicted solids based on thermodynamic measurements and models derived from them depend strongly on chemical composition. However, small aqueous aerosols remain meta-stable with decreasing RH until reaching a crystallization relative humidity(CRH). In contrast, solid aerosols t e up water at the thermodynamically favored deliquescence relative humidity(DRH). This hysteresis causes a dependence of aerosol phase on RH history. 

Dynamic effects are a potentially important but easily overlooked aspect of heterogeneous catalysis that can nonetheless impact the accuracy of our knowledge and predictions. For example, multiple co-existing meta-stable surface oxide phases have been identified for Pd and Ag interacting with oxygen, which suggests that the catalyst surfaces may be in a state of flux under reaction conditions, adding new uncertainty to the nature of the... 

Note that y phase does not exist as a stable phase at the present temperature and pressure. In other words, if y phase is seen in the structure, then the system is not in die equilibrium, but a meta-stable, non-equilibrium state. However, if the thermodynamic state of the system is changed (e.g., different temperature or pressure), y phase may exist as a stable phase in a certain composition range ... 

TCO films such as ZnO Al, ZnO In, and ZnO Ga are meta-stable materials since the phase segregation (e.g., formation of the oxides of the dopants instead of substitutional incorporation) is favored by thermodynamics. The doping efficiency for magnetron sputtered ZnO Al films is usually below 50%. Doping efficiency up to 100% has been reported for films by PLD [79],... 

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