Phase Transition and Spin-gap Behavior in a Layered Tetragonal Pnictide Oxide

Abstract Spin-gap behavior has been observed for the first time in the layered tetragonal compound Na 2 Ti 2 Sb 2 O. Na 2 Ti 2 Sb 2 O shows a sharp discontinuity in magnetic susceptibility at 150 K, reminisent of behavior observed in the spin–Peierls compound CuGeO 3 . Na 2 Ti 2 Sb 2 O also shows a discontinuity in temperature-dependent resistivity at the magnetic transition and metallic behavior for all other temperatures, 5.7 mΩ·cm at room temperature. Ti–Sb–Ti superexchange is proposed to be favored over Ti–O–Ti superexchange, based on the high-temperature magnetic susceptibility data and on the identity of the magnetic orbitals.