Electronic and Magnetic Properties of d 1 Pnictide-Oxides: Na 2 Ti 2 P n 2 O ( P n = As, Sb)
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Electronic and Magnetic Properties of d1 Pnictide-Oxides: Na2Ti2Pn2O (Pn = As, Sb) Tadashi C. Ozawa1, Mario Bieringer2, John E. Greedan2 and Susan. M. Kauzlarich1 1 University of California One Shields Avenue Davis, CA 95616, U.S.A. 2 Institute for Materials Research McMaster University Hamilton, Ontario L8S 4M1, Canada ABSTRACT Bulk physical properties of layered pnictide-oxides, Na2Ti2Pn2O (Pn = As, Sb) have been characterized. Both As and Sb compounds exhibit anomalous transitions in temperature dependent magnetic susceptibility and electrical resistivity. The powder neutron diffraction data show no superlattice reflections indicative of long-range order. The origin of the physical property anomalies and structure-property relationship between As and Sb compounds are described in terms of a charge-density-wave/spin-density-wave mechanism.
INTRODUCTION Na2Ti2 Pn2O (Pn = As, Sb) are layered pnictide-oxide compounds that were first discovered by Adam et al. in the early 90’s [1]. To our knowledge, this is the only pnictide-oxide containing Ti3+, a d1 transition metal. Geometrically, the structure of Na2Ti2Pn2O (Figure 1) is the K2NiF4 type; however, positions of cations and anions are reversed from those in K2NiF4 type compounds. Thus, the chemical structure of this compound should be classified as the antiK2NiF4 type. We have previously measured the temperature dependent magnetic susceptibility and electrical resistivity of the Sb compound, Na2Ti2Sb2O, and have discovered that this compound exhibits a sharp drop in magnetic susceptibility and a metal-to-metal transition in the electrical resistivity at Tc ~ 120 K reminiscent of CDW/SDW materials [2, 3]. In this paper, we report further investigations of the Na2Ti2Pn2O system by synthesizing the bulk sample of the As compound, and comparing its physical properties to that of the Sb compound. For both Sb and As compounds, electrical resistivity and magnetic susceptibility were measured under various temperatures and magnetic fields. Also, temperature dependent powder neutron diffraction has been performed. The results from these experiments as well as the effect of Pn3- on the physical properties of Na2Ti2Pn2O system will be discussed.
EXPERIMENT Bulk samples were prepared by solid state sintering of Na2O, Ti and As or Sb [3]. The field and temperature dependent magnetization was measured on a commercial SQUID-magnetometer (MPMS XL, Quantum Design). The temperature dependence was measured at 10,000 Oe, and GG4.1.1 Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 16 Jan 2020 at 11:47:16, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-658-GG4.1
Figure 1. A perspective view of the structure of Na2Ti2Pn2O (Pn = As, Sb) showing alternation of 2∞[Ti4/2Pn2O4/4]2- layers and double layers of Na+. the field dependent magnetization was measured above and below the Tc for both compounds. For all the magnetic property measurements, about 0.1 g of the sample was used,
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