Self-Propagating Metathesis Routes to Metastable Group 4 Phosphides

Abstract

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.

On the feasibility of phosphide generation from phosphate reduction: The case of Rh, Ir, and Ag

“…The use of molten media or exploitation of vapor transport processes using multizoned furnaces can decrease the heating time and result in well-formed crystals [10]. Solidstate metathesis [11,12] and solvothermal synthesis [13][14][15] are faster methods for generating transition-metal phosphides and can be tuned to prepare materials that are microcrystalline or nanocrystalline. Finally, the decomposition of organometallic precursors has been used extensively for the formation of dispersed phosphide nanoparticles within silica matrices [16,17], or in coordinating solvents [18][19][20][21][22][23].…”

The Synthesis of Metal Phosphides: Reduction of Oxide Precursors in a Hydrogen Plasma

“…[3] A variety of methods for synthesizing bulk metal phosphides, including direct reaction of the appropriate elements for prolonged periods at high temperature, reaction of phosphine with metals or metal oxides, reduction of metal phosphates by hydrogen, electrolysis of molten metal phosphate salts, solid-state metathesis, thermal decomposition of single-source precursors, and self-propagation high-temperature synthesis, are known. [4][5][6] These methods typically require extremely high reaction temperatures (sometimes above 1000 8C) and/or long reaction times. Metal phosphides can be obtained under milder conditions in a solvothermal approach, but this method is not feasible for the deposition of metal phosphides on supports, and in cases where yellow phosphorus and sodium are employed, care must be taken to ensure the rigorous absence of oxygen and water.…”

Dual-source chemical vapour deposition of titanium(III) phosphide from titanium tetrachloride and tristrimethylsilylphosphine

“…Lower temperature CVD reactions utilising both single-source [6] and dual-source approaches [7] from the reaction of TiCl 4 and PH 2 R (R = cyclohexyl or t-butyl) have been investigated. Tristrimethylsilylphosphine (TTMSP) is a functional equivalent of phosphine (PH 3 ) [8] and has been used for the synthesis of main-group single-source precursors to phosphide semiconductors [9] such as the thermolysis of [Cl 2 GaP(SiMe 3 ) 2 ] 2 leading to gallium phosphide (GaP) [10].…”