New cathode candidate Na 2 FeP 2 O 7 for rechargeable sodium ion second battery was successfully prepared by glass-ceramics method. The precursor glass, which is same composition in Na 2 FeP 2 O 7 , was prepared by melt-quenching method. Na 2 FeP 2 O 7 was obtained by heat treatment of precursor glass powder with 10% glucose addition as reduction agent of Fe 3+ at 620°C for 3 h in electric furnace. Na 2 FeP 2 O 7 has triclinic P1-structure with a = 0.64061 nm, b = 0.938893 nm, c = 1.09716 nm, ¡ = 64.5381°, ¢ = 86.0580°, £ = 73.0619°. By means of electrochemical chargedischarge testing, Na 2 FeP 2 O 7 exhibits 2.9 V, 88 mAh/g, in which is 90% for the theoretical capacity during 2.03.8 V cut-off voltages. Na 2 FeP 2 O 7 ceramics has the potential for the safety cathode candidate for the sodium ion battery with a low materials cost.
The electrochemical property of tin-phosphate (designate as GSPO) glass anode for the sodium ion battery was studied. During the first charge process, sodium ion diffused into GSPO glass matrix and due to the reduction of Sn2+ to Sn0 state sodiated tin metal nano-size particles are formed in oxide glass matrix. After the second cycle, we confirmed the steady reversible reaction ∼320 mAh/g at 0–1 V cutoff voltage condition by alloying process in NaxSn4. The tin-phosphate glass is a promising candidate of new anode active material that realizes high energy density sodium ion batteries.
Temperature dependent crystal structures of the quasi-one-dimensional ladder material BaFe 2 Se 3 are examined. Combining the optical second harmonic generation (SHG) experiments and neutron diffraction measurements, we elucidate the crystal structure with P mn2 1 space group in the lowtemperature phase below T s2 = 400 K, further above Néel temperature. This low-temperature phase loses the spatial inversion symmetry, where a resultant macroscopic polarization emerges along the rung direction. The transition is characterized by block-type lattice distortions with the magneto-striction mechanism. Change in the electrical resistivity and the magnetic susceptibility across the polar-nonpolar transition also suggests a modification of the electronic states reflecting the structural instability. Consistency and discrepancy with the existing theory are discussed. arXiv:1902.10900v1 [cond-mat.str-el]
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