Synthesis, Crystal Structure, and Properties of the Alluaudite-Type Vanadates Ag_2–xNa_xMn₂Fe(VO₄)₃

Abstract

The new members of the Ag2-xNaxMn2Fe(VO4)3 (0 ≤ x ≤ 2) solid solution were synthesized by a solid-state reaction route, and their crystal structures were determined from single-crystal X-ray diffraction data. The physical properties were characterized by Mössbauer and electrochemical impedance spectroscopies, galvanostatic cycling, and cyclic voltammetry. These materials crystallize with a monoclinic symmetry (space group C2/c), and the structure is considered to be a new member of the AA'MM'2(XO4)3 alluaudite family. The A, A', M, and X sites are fully occupied by Ag(+)/Na(+), Ag(+)/Na(+), Mn(2+), and V(5+), respectively, whereas a Mn(2+)/Fe(3+) mixture is observed in the M' site. The Mössbauer spectra confirm that iron is trivalent. The impedance measurements indicate that the silver phase is a better conductor than the sodium phase. Furthermore, these phases exhibit ionic conductivities 2 orders of magnitude higher than those of the homologous phosphates. The electrochemical tests prove that Na2Mn2Fe(VO4)3 is active as positive and negative electrodes in sodium-ion batteries.

Thermal Perturbation Nucleation and Controllable Growth of Silver Vanadate Crystals by Dynamic Template Route

“…37 V 2p 5/2 and V 2p 3/2 of V 5+ in Ag 4 V 2 O 7 nanotube clusters were observed at 516.83 and 524.58 eV (Figure 3d). 38,39 The XPS also showed the elementary composition of Ag 4 V 2 O 7 nanotube clusters (Table 1).…”

“…The binding energy at 368.06 and 374.07 eV were ascribed to Ag + , and others at 368.59 and 374.56 eV were assigned to Ag 0 . − The O 1s XPS spectrum in Figure c showed a peak at 530.03 eV, indicating the bond of V–O . V 2p 5/2 and V 2p 3/2 of V 5+ in Ag 4 V 2 O 7 nanotube clusters were observed at 516.83 and 524.58 eV (Figure d). , The XPS also showed the elementary composition of Ag 4 V 2 O 7 nanotube clusters (Table ).…”

Structural properties of the alluaudite-type materials Ag2– x Na x Mn3(VO4)3 (x=0.62 and 1.85)

“…The Ag 2−x Na x Mn 3 (VO 4 ) 3 compounds crystallize with the well-known alluaudite-type structure as do Ag 2 Mn 3 (VO 4 ) 3 and Ag 2−x Na x Mn 2 Fe(VO 4 ) 3 [20,21]. In this structure the octahedra share edges end form MnO 4 infinite chains along the [101 ̅ ] direction (Fig.…”

“…Among these materials, perhaps Na 2+x Fe 2−y (SO 4 ) 3 is the most interesting for NIBs since it operates at a relatively high voltage of 3.8 V (vs. Na). To our knowledge, no alluaudite vanadates were reported so far as electrodes for Li-or Na-ion batteries, except Ag 2−x Na x Mn 2 Fe(VO 4 ) 3 [20]. These materials have shown higher ionic conductivities as compared to the homologous phosphates.…”

Unlocking New Redox Activity in Alluaudite Cathodes through Compositional Design

“…Additionally, the larger Mn-O bond length variation for M(2)O6 octahedra is consistent with the presence of Jahn-Teller distorted Mn 3+ species with a high spin d 4 electronic configuration. 68 Na occupies two unique sites in the structure, Na(1) and Na (2), which span separate 1D tunnels along the c axis and allow for Na diffusion through the structure. -b show SXRD patterns collected on Na2Mn3(VO4)3 synthesized at 500°C and 300°C, respectively.…”