Spectroscopic investigations of nanosized Cr3+ doped Sc2-x Inx (WO4 )3 : A new promising laser material.

Chromium(III) doped nanosized Sc2-x Inx (WO4 )3 , (x = 0-2) solid solutions were prepared by the co-precipitation/calcination method. The obtained powders were characterized using X-ray diffraction (XRD), electron paramagnetic resonance (EPR), infrared (IR), absorption and luminescence spectra. X-ray analysis showed that the compounds are pure solid solutions with orthorhombic symmetry at x values 0 and 0.5 and with monoclinic symmetry for x values 1.0, 1.5 and 2.0. The calculated crystallite size ranged from about 20 to 110 nm, except for Sc2 (WO4 )3 characterized by considerably larger sizes. IR spectra of the solid solutions contain the characteristic vibrations of the WO4 and MeO6 , (Me = Sc, In) polyhedra, building the Sc2 (WO4 )3 and In2 (WO4 )3 structures. EPR analysis proved the presence of isolated Cr3+ ions in the crystal field with rhombic symmetry. The presence of Cr3+ in sites with weak and strong crystal field was revealed by absorption and luminescence spectra. This study demonstrates the effect of hosts crystal symmetry, particles size and doping concentration on the luminescence properties.

Redox properties of alluaudite sodium cobalt manganese sulfates as high-voltage electrodes for rechargeable batteries.

Alluaudite sulfates are predicted to be high-voltage electrodes for lithium- and sodium-ion batteries. Herein, we provide the first experimental evidence for the operation of sodium cobalt-manganese sulfate, Na2+2δ(Co0.63Mn0.37)2-δ(SO4)3, at potentials higher than 4.0 V vs. Li/Li+. This fact comes as a result of the reduced cationic deficiency, redox properties of Co and Mn and stability of the alluaudite structure during alkali ion intercalation.

Combined use of EPR and 23Na MAS NMR spectroscopy for assessing the properties of the mixed cobalt-nickel-manganese layers of P3-NayCo1-2xNixMnxO2.

Knowledge on the formation of mixed transition metal layers on lithium and sodium transition metal oxides, Li/Na(Co,Ni,Mn,)O2, determines the ability to control their electrochemical properties as electrode materials in alkaline ion batteries. Taking this into account, herein we combine the EPR and 23Na MAS NMR spectroscopic techniques to gain insights into the structural peculiarities of the mixed cobalt-nickel-manganese layers of NayCo1-2xNixMnxO2 with a three-layer stacking (P3-type) structure. Two types of compositions are examined where diamagnetic Co3+ and paramagnetic Ni3+ and Mn4+ are stabilized: Na2/3Co1/3Ni1/3Mn1/3O2 and Na1/2Ni1/2Mn1/2O2. EPR spectroscopy operating in the X- and Q-band region is applied with an aim to improve the spectra resolution and, on the other hand, to provide straightforward information on the coordination of the transition metal ions inside the layers. The analysis of EPR spectra is based on the reference for the Mn4+ and Ni2+ ions occurring simultaneously in oxides with two layer stacking, P2-Na2/3Ni1/3Mn2/3O2. Complementary to EPR, 23Na MAS NMR spectroscopy at high spinning rates is undertaken to assess the local structure of the Na nucleus in the layered P3-NayCo1-2xNixMnxO2 oxides. All results are discussed taking into account the EPR and NMR data for the well-known lithium analogues O3-LiCo1/3Ni1/3Mn1/3O2 and O3-LiNi1/2Mn1/2O2. Finally, the structure peculiarities of the transition metal layers extracted from the EPR and NMR methods are demonstrated by electrochemical intercalation of Li+ ions into P3-NayCo1-2xNixMnxO2.