Structure and Physical Properties of the Layered Titanium-Based Pnictide Oxides (EuF)₂Ti₂Pn₂O (Pn = Sb, Bi)

We report two novel titanium-based pnictide oxide compounds (EuF)₂Ti₂Pn₂O (Pn = Sb, Bi), which are synthesized by replacing Sr²⁺ in (SrF)₂Ti₂Pn₂O [Liu, R. H. Structure and Physical Properties of the Layered Pnictide-Oxides: (SrF)₂Ti₂Pn₂O (Pn = As, Sb) and (SmO)₂Ti₂Sb₂O. Chem. Mater. 2010, 22, 1503-1508] with Eu²⁺ using a solid-state reaction. (EuF)₂Ti₂Sb₂O exhibits an obvious anomaly in resistivity and heat capacity at T ∼ 195 K, which may arise from the spin-density wave/charge-density wave instability. Similar features are also observed in BaTi₂Pn₂O, (SrF)₂Ti₂Pn₂O, and Na₂Ti₂Pn₂O (Pn = As and Sb) [Liu, R. H. Structure and Physical Properties of the Layered Pnictide-Oxides: (SrF)₂Ti₂Pn₂O (Pn = As, Sb) and (SmO)₂Ti₂Sb₂O. Chem. Mater. 2010, 22, 1503-1508, Ozawa, T. C. Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors. Sci. Technol. Adv. Mater. 2008, 9, 033003, Wang, X. F. Structure and physical properties for a new layered pnictide-oxide: BaTi₂As₂O. J. Phys.: Condens. Matter. 2010, 22, 075702, and Xu, H. C. Electronic structure of the BaTi₂As₂O parent compound of the titanium-based oxypnictide superconductor. Phys. Rev. B 2014, 89, 155108]. Magnetic susceptibility measurements indicate an antiferromagnetic transition at T ∼ 2.5 K for (EuF)₂Ti₂Sb₂O. In particular, the electronic specific heat coefficients of both (EuF)₂Ti₂Sb₂O and (EuF)₂Ti₂Bi₂O are significantly enhanced compared to those of (SrF)₂Ti₂Pn₂O, Na₂Ti₂Pn₂O, and BaTi₂Pn₂O,^1,5,6 which may be due to a strong electron correlation effect in this system. Thus, (EuF)₂Ti₂Pn₂O (Pn = Sb, Bi) may provide new platforms for studying density wave, magnetic ordering, and electron correlation effects.