Component interactions in {Y, Gd, Tm}-Mo-B ternary systems at 1270 K

X-ray structure analysis has been used to construct isothermal sections at 1270 K for the phase diagrams for the Y - Mo - B and Tm - Mo - B systems. T he solubility of MoB2 in YB2 is low, while that in TmB2 is not more than 0. 05 molar fraction (lattice constants of the (Tm, Mo)B-2 phase with the AlB2 structure and limiting composition a = 0.3253(2), c = 0.3678(4) nm). The e xistence of some previously known borides is confirmed, and the lattice par ameters for some of them have been refined: YMoB4 (space group Pbam, struct ure type YCrB4, a = 0.6038(1), b = 1.1672(2), c = 0.36170(7) nm), YMo3B7 (P nma, own structure type), GdMoB4 (Pbam. type YCrB4, a = 0.60531(6), b = 1.1 700(1), c = 0.36355(6) nm), Tm2MoB6 (Pbam, type Y2ReB6), TmMo3B7 (Pnma, typ e YMo3B7). New ternary compounds have been identified. Y3MoB7 (Cmcm, type E r3CrB7 a = 0.34775(2), b = 1.59793(5), c = 0.94757(2) nm), Gd3MoB7 (type Er 2CrB7, a = 0.3497(2), b = 1.6157(6), c = 0.9516(5) nm), and TmMoB3 (P2(1)/m , type ErMoB3, a = 0.6771(2), b = 0.3142(1), c = 0.5373(1), beta = 101.48(2 )degrees). The parameters of the metal atoms and their isotropic temperatur e factors have been refined for Y3MoB7 (DRON-3M diffractometer, N-hkl = 288 , R = 0.106).