Homogeneity Range and Preparation

Vapor pressure measurements and X-ray studies on samples with compositions GdSei 53 to GdSe2.o2 indicated the existence of only one polyselenide phase, with variable composition between GdSei 775 and GdSei 862. Veale, Barrett [1]. The occurrence of an unstable diselenide, GdSe2, is claimed by Vickery, Muir [2, 3], see the phase diagram p. 276. 

A nonstoichiometric black polyselenide GdSe i e obtained by heating Gd filings and Se powder in an open tube first to 350°C, then slowly (2 K/min) to 500 C, and at last quickly to 1000°C. Excess Se is removed by distillation, Sokolov etal. [4]. 

The magnetic susceptibility x of GdSe2 at 77 to 900 K follows the Curie-Weiss law with p = -3Kand eff = 7.76 iq, Pechennikov etal. [9]. A value Xmoi = 4760x10 cm /mol is given for room temperature. The resistivity is q = 6400 and 12500 jiQ cm at 200 and 600°C, respectively the Seebeck coefficient a=150 and 205 xV/K at the same temperatures. Preliminary Hall measurements confirm the assumption of p-type conductivity [3]. 

The samples have a cubic ThsP4 type structure with a = 8.706 A. They contain 0.24 excess electrons per M and are ferromagnetic with 0p = 47 K, [left = 7.96 Methfessel [2], Holtzberg 

A series of (Gd,Nd)Sei 5 alloys were prepared by reacting the elements at 1010°C in evacuated quartz vials for 100 h. The products consisted of a cubic phase (presumably NdSei 5) and an orthorhombic phase (presumably GdSSi 5). The reaction products were hot-pressed at 1500°C and 352 atm for 10 min. This yielded a material that consisted of two cubic phases with very similar lattice parameters. Samples of the compositions Gdo.io2Ndo.899Sei 493, 

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Little information is available on homogeneity ranges and defect structures in the dodecaborides. The only variation from stoichiometry in these borides is for YB,2i the limiting phase determined by density measurements is Yq92B,2. This result can be attributed to the size of Y which is the maximum for metals that form the dodecaborides. Attempts to prepare DyB,2 with a nonstoichiometric composition are conclusive. ... 

The sol-gel technique was also used to prepare solid electrolytes containing MEEP, triethoxysilane (TEOS) and lithium triflate. Homogeneous, transparent and mechanicaUy stable materials have been obtained by Gughelmi [611] from a partially hydroxylated MEEP and TEOS, which after doping with LiSOjCFj exhibited a conductivity in the range 3x10 S cm at 60 °C. 

The pore size and distribution in the porous particles play essential roles in NPS synthesis. For example, only hollow capsules are obtained when MS spheres with only small mesopores (<3 nm) are used as the templates [69]. This suggests that the PE has difficulty infiltrating mesopores in this size range, and is primarily restricted to the surface of the spheres. The density and homogeneity of the pores in the sacrificial particles is also important to prepare intact NPSs. In a separate study, employing CaC03 microparticles with radial channel-like pore structures (surface area 8.8 m2 g 1) as sacrificial templates resulted in PE microcapsules that collapse when dried, which is in stark contrast to the free-standing NPSs described above [64]. 

An examination of the magnetic susceptibility, thermal analysis characteristics, and X-ray powder patterns of samples of V02+ c( — 0.02 x < 0.03) prepared by heating V205-V203 mixtures in silica tubes has shown that the homogeneity range for V02 is very narrow.393"... 

Both systems are suitable to check whether or not there is a directly proportional relationship between the width of the homogeneity range of a compound and the growth rate of its layer, predicted by the diffusional theory.5 It is clear that in view of the presence of the liquid zinc phase during preparation of Ni-Zn and Co-Zn reaction couples, all the inter-metallic phases had equal and favourable conditions to form their nuclei at the interface between nickel or cobalt and zinc, which could then readily grow during subsequent isothermal annealing. 

Reimers and Schork [94, 95] report the use of PMMA to stabihze MM A miniemulsions enough to effect predominant droplet nucleation. Emulsions stabilized against diffusional degradation by incorporating a polymeric costabilizer were produced and polymerized. The presence of large numbers of small droplets shifted the nucleation mechanism from micellar or homogeneous nucleation, to droplet nucleation. Droplet diameters were in the miniemulsion range and reasonably narrowly distributed. On-hne conductance measurements were used to confirm predominant droplet nucleation. The observed reaction rates were dependent on the amount of polymeric costabilizer present. The latexes prepared with polymeric costabilizer had lower polydispersities (1.006) than either latexes prepared from macroemulsions (1.049) or from alkane-stabilized miniemulsions (1.037). 

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