PHASE-TRANSITION AND SPIN-GAP BEHAVIOR IN A LAYERED TETRAGONAL PNICTIDE OXIDE

Spin-gap behavior has been observed for the first time in the layered tetragonal compound Na2Ti2Sb2O. Na2Ti2Sb2O shows a sharp discontinuity in magnetic susceptibility at 150 K, reminisent of behavior observed in the spin-Peierls compound CuGeO3. Na2Ti2Sb2O also shows a discontin uity in temperature-dependent resistivity at the magnetic transition a nd metallic behavior for all other temperatures, 5.7 m Omega . cm at r oom temperature. Ti-Sb-Ti superexchange is proposed to be favored over Ti-O-Ti superexchange, based on the high-temperature magnetic suscept ibility data and on the identity of the magnetic orbitals. (C) 1997 Ac ademic Press.