Structural and magnetic properties of frustrated GaxMn(3-x)O4(1.2 ≤ x ≤ 1.6) spinels

International audienceWe report a systematic study of the structural and magnetic properties of frustrated compounds of GaxMn(3−x)O4 (1.2 ≤ x ≤ 1.6) prepared by solid-state reaction. Using Rietveld refinement of X-ray diffraction patterns and O'Neill-Navrotsky model, we demonstrate that the system GaxMn(3−x)O4 (1.2 ≤ x ≤ 1.6) is an inverse spinel with low inversion parameter, in which Ga3+ replaces Mn3+ cations located in B-sites. The inverse magnetic susceptibility, the shape of ZFC/FC magnetization curves at low temperatures, the existence of hysteresis in all compounds, the frustration parameter and the spontaneous magnetization analysis show that the compounds with x = 1.2–1.4 exhibit a non-collinear ferrimagnetic order and the compounds with x = 1.5–1.6 exhibit a frustrated non-collinear ferrimagnetic order. Spin wave stiffness parameters were determined for each composition using the fitting results of spontaneous magnetization curves. It is demonstrated that for the compounds x = 1.2–1.4 with a non-frustrated ferrimagnetic order, the change of spontaneous magnetization Ms(T) obeys to Bloch's law (T3/2). For x = 1.5–1.6, the compounds exhibit a frustrated ferrimagnetic order, and the Ms(T) shows a deviation from Bloch's law

Comparative Study of Sb2O3 (Sb2O5) and Ta2O5 Doping Effects with TeO2 on Electrical Properties of delta-Bi2O3

23rd Conference on Applied Crystallography, Krynica Zdroj, POLAND, SEP 20-24, 2015International audienceIn this study, Sb2O3 (Sb2O5) and Ta2O5 are used as co-dopants with TeO2 to stabilize the delta phase of bismuth oxide (delta-Bi2O3). Some compositions with formula (1 x) BiO1.5-(x /4) Sb2Te2O9 and (1 - x) BiO1.5-(x/4) Ta2Te2O9 (x = 0.1, 0.2, 0.3, 0.6, and 0.9) have been synthesized by solid state reaction at 850 degrees C and characterized by powder X-ray diffraction. The Bi0.9Sb0.05Te0.05O1.575, Bi0.9Ta0.05Te0.05O1.575 and Bi0.8Ta0.1Te0.1O1.65 retain a cubic fluorite structure of delta-Bi2O3 phase. The electric properties were studied by impedance spectroscopy. All samples were evaluated by calculating conductivities and activation energies. Various impedance model including constant phase element and the Warburg impedances have been used to interpret the Nyquist representations of electrical analyses

Sodium intercalation/de-intercalation mechanism in Na4MnV(PO4)3 cathode materials

Na4MnV(PO4)3 is a sodium ion conducting material with a NASICON type crystal structure. This phase is not much known as an electrode material. The present work focuses on the sodium ion intercalation/de-intercalation mechanism and charge/discharge behavior of the material. The Na4MnV(PO4)3 is synthesized through a sol-gel process and characterized by XRD, SEM, and XPS. The structural analysis confirms the formation of a phase pure crystalline material with nanometric particle size which adopts a trigonal crystal structure. Galvanostatic intermittent titration technique (GITT) measurements indicate that Na4MnV(PO4)3 is electrochemically active having slanting voltage plateaus. Ex-situ and In-situ XRD analysis, as a function of sodium concentration, indicate that the intercalation/de-intercalation of sodium is associated with a single-phase reaction rather than a biphasic reaction when cycled between 1.5 and 4.5 V. The electrochemical measurements on composite electrodes, Na4MnV(PO4)3/CNTS (1 & 3 wt.%), show promising charge/discharge capacity (?140 mAh/g), good cyclability (100% capacity retention after 40 cycles) and reasonable rate capability. The cyclic voltammetry (CV) and X-ray Photoelectron Spectroscopy (XPS) analyses indicate that the main contributions towards the activity of Na4MnV(PO4)3 can be attributed to the active of Mn2+/Mn3+ and V3+/V4+ redox couple with partial activity of V4+/V5+. The obtained results suggest that Na4MnV(PO4)3 is a promising electrode material which can be achieved better rate performance with long cycling stability and battery performance through engineering of the particle morphology and microstructure. � 2018 Elsevier LtdThe authors acknowledge the financial support from the Center for Advanced Materials (CAM), Qatar University, Doha, Qatar. The authors would also like to thank Mar�a J�uregui and Damien Saurel from XRD platform at CIC Energigune for her help for the in situ-XRD measurements. Appendix AScopu