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Group 4 phosphides, which are typically prepared at high temperatures (> 800 degrees C) over several days, are synthesized in self-propagating metathesis (exchange) reactions in seconds. These reactions produce cubic forms of zirconium phosphide (ZrP) and hafnium phosphide (HfP) which are normally made at temperatures greater than 1425 degrees C and 1600 degrees C, respectively. To test whether the high temperatures reached in the metathesis reactions are responsible for the formation of the cubic phases, inert salts are added to lower the maximum reaction temperatures. The lower temperature reactions still result in cubic phosphides, although smaller crystallites form. Further experiments with phosphorus addition indicate that the phosphorus content is not responsible for cubic phase formation. Templating is ruled out using lattice mismatched KCl and hexagonal ZnS as additives. Therefore, the direct synthesis of the high-temperature cubic phase in metathesis reactions appears to be caused by nucleation of the metastable cubic form that is then trapped by rapid cooling. Heating the cubic phase of either ZrP or HfP to 1000 degrees C for 18 h, or carrying out metathesis reactions in sealed ampules at 1000 degrees C, results only in the hexagonal phase.

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Small crystallites of CdTe have been produced using a new solution synthetic method. In this technique, Cdl2 and Na2Te are each dissolved separately in methanol before rapid mixing. The product of this reaction is pure, stoichiometric CdTe with interesting electronic and optical properties. Photoluminescence studies of this material show a blue shift due to the quantum confinement, indicating the presence of small crystallites. Transmission electron microscopy confirms the presence of nanocrystals. Reaction temperature and processing conditions can be varied to change the crystallite sizes produced. This synthesis can also produce nanocrystalline HgTe.

Self-Propagating Metathesis Routes to Metastable Group 4 Phosphides.-Group 4 phosphides MP (M: Ti, Zr, Hf) are synthesized in self-propagating metathesis (exchange) reactions from Na 3 P and the metal halides MCl 4 (M: Zr, Hf) or TiI 4 . The reactions are carried out in a stainless steel reaction vessel and are ignited with a hot wire. Reactions are also carried out in sealed evacuated quartz tubes at 1000 • C for 18 h. The products are characterized by powder XRD. Whereas sealed tube reactions lead exclusively to the low-temperature hexagonal phase of MP, the self-propagating reactions lead to the high-temp. metastable cubic phase of ZrP and HfP. The process by which the cubic phases form is discussed. -(JARVIS JR., ROBERT F.; JACUBINAS, RICHARD M.; KANER, RICHARD B.; Inorg. Chem. 39 (2000) 15, 3243-3246;