Chemical transport reactions of some rare earth phosphides: syntheses of new rare earth-silicon-phosphorus ternary compounds

Abstract

Attempts have been made to grow single crystals of new rare earth polyphosphides of La, Ce and Pr by chemical transport reactions, using iodine as the transporting agent in a closed, fused-silica ampoule. Crystals of PrP, PrP 2 and PrP 5 were grown by this method and a structural investigation carried out by the precession method. At high temperatures, however, the silica ampoule was found to be attacked and, in consequence, silicon was introduced into the crystals. The crystals were studied by the precession method and by electron-probe microanalysis, and proved to be new, rare earth-silicon-phosphorus ternary compounds. These ternary crystals can be described as follows: 1. (1) CeSiP 3, space group C2ma, Cm2a or Cmma, a = 5.867 +- 0.002 A ̊ , b = 5.718 +- 0.002 A ̊ , c = 12.656 +- 0.005 A ̊ , d obs ., 4.09 g/cm 3 (this type of phase structure was also obtained for Pr); 2. (2) LaSi 2P 6, space group C2cm, Cmc2, or Cmcm, a = 10.150 +- 0.002 A ̊ , b = 28.189 +- 0.006 A ̊ , c = 10.385 +- 0.003 A ̊ , d obs ., 3.38 g/cm 3 (this type of phase was also obtained for the Ce-Si-P system); 3. (3) nonstoichiometric ternary compounds obtained for La and Ce, space group F2mm, Fm2m, Fmm2, F222 or Fmmm, a = 5.190 +- 0.002 A ̊ , b = 5.776 +- 0.002 A ̊ , c = 25.060 +- 0.004 A ̊ (these parameters were measured for a Ce-Si-P ternary sample).