ИСТИНА

Most of R2T2X phases crystallize in the four structure types: Mo2B2Fe (tetragonal, P4/mbm), Er2Au2Sn or U2Pt2Sn (tetragonal, P42/mnm) - a superstructure of Mo2B2Fe, W2B2Co (orthorhombic, Immm), and Mn2B2Al (orthorhombic, Cmmm) [1]. Five less common types are encountered in literature. Two of these are monoclinic ones: HT-Pr2Co2Al or Ca2Ir2Si (C2/c) - stacking variant of the W2B2Co [2,3] - and LT-Nd2Cu2Cd (C2/c, own structure type) - superstructure of Mn2B2Al [4]; the other three structures are orthorhombic: La2Ni3 (Cmce) [5], o-La2Ni2In (Pbam) [6], and Ca2Pd2Ge (Fdd2) [7]. Only a few representatives of these types are reported to date. The structural diversity of the R2T2X family is frequently accompanied by polymorphic phenomena between these structure types. We report on the synthesis and crystal structure of the new ternary intermetallic Ce2Rh2Ga. Its formation and dimorphism have been investigated by powder and single crystal X-ray diffractometry, as well as by differential thermal analyses. LT- and HT-Ce2Rh2Ga can be obtained by the chosen respective thermal treatment. The HT-Ce2Rh2Ga, stable above 864(5)C, is orthorhombic La2Ni3-type ; the LT-Ce2Rh2Ga, stable below this temperature, is monoclinic Pr2Co2Al - (Ca2Ir2Si-) type