Cooling single crystals

Prolonged standing in a THF solution results in its decomposition as outlined above however, by brief warming in THF followed by slow cooling, single crystals of the compound have been obtained. Its molecular stereochemistry is meridional in the solid state.9 Substitution reactions of the THF ligand by phosphine and halide ligands have been described.9,15... 

Depending on the choice of solvent, the temperature of dissolution and the rate of cooling, single crystals with at least two well differentiated morphologies could be obtained in a reproducible manner. 

At 200°C a transformation to another rhombohedral modification takes place with a lattice contraction 4c = -1.85% and 4a = -0.8%. At 205°C the cell of /3-In2Se3 has a = 4.00 A, c = 28.33 A [456]. Thermal expansion coefficients are very similar for both modifications (see Figure 103). On cooling, single crystals transform back to the a-phase at 90 to 60 °C. Powdered samples and pressed pellets, however, can be supercooled down to room temperature and this probably holds also for the films studied by Semiletov [446, 448] though this /3-phase has not the same unit cell as Semiletov s. 

Germanium [7440-56-4] M 72.6, m 937 , 925-975 , b 2700 , d 5.3. Copper contamination on the surface and in the bulk of single crystals of Ge can be removed by immersion in molten alkali cyanide under N2. The Ge was placed in dry cyanide powder in a graphite holder in a quartz or porcelain boat. The boat was then inserted into a heated furnace which, after a suitable time, was left to cool to room temperature. At 750°, a 1mm thickness requires about Imin, whereas 0.5cm needs about half hour. The boat was removed and the samples were taken out with plastic-coated tweezers, carefully rinsed in hot water and dried in air [Wang J Phys Chem 60 45 7956]. 

Figure 4. Thennal strain for a single-crystal Nio625Alo 3 5 alloy measured on cooling along three (lOO directions in a capacitance dilatometer. The inset shows in detail the data in the temperature range 100-250K (From reference 6)...

Single crystals of RbsNbgOFig can be grown successfully by dissolving the prepared compound in a 20-30% HF solution at increased temperature and subsequent slow cooling of the solution down to room temperature. The solubility of RbgNbjOFjg in 20% HF solution versus the temperature of the solution is given in Fig. 7. 

Using powder as a starting material, single crystals were grown from a solution of hydrofluoric acid containing appropriate concentrations of each type of compound (M = K or Rb), using the slow cooling method [206, 209, 211,438],... 

Some measurements with Pt single-crystal faces have been published recently.140,210,773 Iwasita and Xia210 prepared platinum single crystals according to the method of Clavilier et a/.186 773 After flame annealing and cooling in an H2 + Ar mixture, the electrode was protected... 

Other single-crystal x-ray diffraction studies of transition element dopants in jS-rh boron are based on the results of a refinement of the /3-rh boron structure that establishes the occurrence of four new low-occupancy (3.7, 6.6, 6.8 and 8.5%) B positions in addition to the earlier known ones. The dopant elements studied, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Hf and Ta, do not enter B positions in the framework, but they enter the Al, A2, D and E positions. In some cases the doping elements have been studied at several concentrations for each element and for different cooling rates. The percentage occupancies of certain positions are eorrelated with the atomie sizes of the dopants. The bond distances between the polyhedra are shorter than those within the polyhedra. The mechanism of doping for some cases is denoted displacive, rather than interstitial or substitutional, because of competing interactions between the six different partially occupied B positions and dopant atoms. 

The compounds of Mg with Ca, Sr and Ba are also simply prepared mixtures of different proportions are heated to above the liquidus temperature and cooled for examination under inert conditions. Single crystals can be picked out from those alloys that contain a distinct compound phase as detected by x-rays. ... 

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