ИСТИНА

Binary borides MeBx are relatively simple regarding their chemical composition and crystal structure but show diverse superconducting behavior that makes them attractive model objects for studying superconducting mechanisms. Metal hexaborides MeB6 adopt the simple CsCl-type Pm3¯m crystal structure. Among hexaboride superconductors only YB6 has the transition temperature achievable by 4He cryogenics. Depending on preparation conditions and methods, the reported critical temperatures of this BCS-type superconductor vary up to 8.4 K. In this report we present 11B and 89Y NMR study performed in 7 T field on YB6 powder samples with Tc = 7.4 and 4.2 K prepared from single crystals grown with a slight variation of the starting charge composition. A recent study of these crystals [1] has related the change in Tc with structural peculiarities: the sample with higher Tc was reported to be slightly more disordered and less stoichiometric that the other one.