On the crystal structure of new series of compounds, RPt2+xSb2-y (x=0.125, y=0.25; R=La, Ce, Pr)

A new compound CePt2+xSb2-y (x=0.125, y=0.25) was synthesized by arc-melting of the elements. The chemical and structural characterizations were carried out at room temperature on as-cast samples using X-ray diffractometry, metallographic analysis and EDS-microanalysis. According to the results of X-ray single crystal diffraction this antimonide crystallizes in I4cm space group (no. 108), Z=32, rho=12.19Mg/m3, mu=89.05mm-1 (a=12.5386(3)A, c=21.4692(6)A (crystal I) and a=12.5455(2)A, c=21.4791(5)A (crystal II)). The structure and composition were confirmed by powder X-ray diffraction (a=12.4901(2)A, c=21.3620(4)A) and EDS-microanalysis respectively. Isotypic compounds were observed with La and Pr from X-ray powder diffraction of as-cast alloys at room temperature (a=12.6266(4)A, c=21.4589(6)A for LaPt2+xSb2-y and a=12.5184(5)A, c=21.4178(7)A for PrPt2+xSb2-y). The CePt2+xSb2-y structure is derived from CaBe2Ge2 (a=2a0-2b0, b=2a0+2b0, c=2c0) and comprises a new atomic arrangement with both vacancy on 4(b) pyramidal site and substitution of antimony atoms (X) by platinum (B) in the B-XX-B layers (referring to the subcell structure) forming two B-1/2B1/2XX-3/4B and two X-BB-X layers per cell. The structure of CePt2+xSb2-y is compared with those reported before for URh1.6As1.9 and CeNi1.91As1.94.