Low-density phases

Now, assume that the adsorbed layer is not a homogeneous phase but exhibits two-phase eoexistenee between the low density phase (1) and the high density phase (2) and that these two phases eontain Ni and N2 mole-eules, respeetively, and oeeupy the areas A j and A2. Of eourse, the total area of the sample is + 2 the total number of adsorbed partieles is... 

Ice films condensed from the water vapour on a cold substrate (T<30 K) has been characterized as a high-density amorphous form of ice, which could be a denser variant of the low-density phase obtained by deposition above 30 K. Condensation from the background pressure also leads to ice films that are highly porous at a nanoscale.This porosity is lost by warming or by direct deposition of water at T>90 K. Warming ice at 150 K induces the crystallization, whatever the initial structure is. 

Narten et al. also deduced from their data that one fifth of the water molecules are located at this additional distance. In a RDF picture, this corresponds to 4 nearest-neighbours at 2.76 A and 1 second neighbour at 3.3 A. This matches well the atomic surrounding depicted by the cluster corresponding to the structure of ice after the irradiation (cluster 2). The local order before the irradiation is better described by the 4-coordinated tetrahedron found in the normal amorphous low-density ice and in the crystalline ice (cluster 1). Thus we conclude that the structure of the ice film before the irradiation is not that of the high-density phase but that of the normal low-density phase. In addition, since the irradiated ice has a local order similar to what expected in the high-density phase, we also conclude that the photolysis at 20 K has induced the phase transition from the low-density to the high-density amorph. 

Notice also that, at temperatures higher than that corresponding to capillary condensation, F (T. pb) increases with decreasing T. Tliis is indicative of a regime where one would observe growth of a wetting film, which at a mean-field level, manifests itself as an increase in overall density of an otherwise homogeneous low-density phase adsorbed all across the slit pore. For temperatures lower than that at which capillary condensation sets in, F (pb) turns out to be nearly independent of T the lower T becomes. This reflects that, when sufficiently close to bulk gas-liquid coexistence, the pore is com-... 

Recently a low density phase of SiC2N4 has been investigated [45] with a possible cubic structure (Pn3rri) shown in Fig. 10. 

Recently, Mahecha-Botero and co-workers presented a generalized comprehensive model which characterizes multiple phases and regions (low-density phase, high-density phase, staged membranes, freeboard region) with the possibility to include new features or simplifications in order to simulate different fluidized bed (membrane) reactors. For a more detailed description of the model and assumptions an interested reader is referred to. ... 

At increased concentrations of alkali, the color changes to bronze-brown. In some temperature ranges, two phases exist. One is similar to the diluted phase and has the highest density of the two. The low-density phase has a higher concentration of metal. This is the bronze-colored phase. 

Study of the system dynamics shows that at very low temperatures the diffusion coefficient in the high-density and low-density phases is zero, characterizing solid amorphous phases (LDA and HD A). Thus, starting from zero temperature at fixed chemical potential, the LDL and the HDL emerge continuously from the LDA... 

Similar to the two-dimensional case, at null temperature, a gas phase and two phases of different densities, LD and HD, may be present, depending on model parameters. The ordered high-density and low-density phases are represented in Fig. 5. As can be seen, in the LD phase only half the lattice is occupied and each particle bonds to all the four nearest neighbors, whereas in the HD phase all the sites are occupied and each molecule forms four bonds. At chemical potential... 

At zero temperature, a gas phase coexists with a low density phase at lower chemical potential, while a low-density phase coexists with a hlgh-density phase at higher chemical potential,... 

Under-coordinated water molecules could form an ice-like, low-density phase that is hydrophobic, stiffer, and thermally more stable than the bulk water [5, 6]. 

According to the BOLS premise [61-64], reducing the molecular CN will shorten and strengthen the H-O covalent bond, and hence, raising the Tmax which, in turn, will lengthen and weaken the 0 H non-bond and thereby cause further O-O expansion and density drop [47]. Therefore, an introduction of the low-density phase or the ring- or chain-like topologies will further elevate the Tinax and lower the density, which could compensate to a certain extent for the deviation between calculations and measurements. 

The supersolid (low density) phase indeed exists but only in regions consisting water molecules with fewer than four neighbors. The supersolidity phase forms because of the H-O bond contraction due to molecular undercoordination and the interelectron-pair repulsion pertaining to 0 H-0 bond. 

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