ABSTRACT
Potassium hexavanadate (K2V6O16·nH2O) nanobelts have been synthesized by the LPE-IonEx method, which is dedicated to synthesis of transition metal oxide bronzes with controlled morphology and structure. The electrochemical performance of K2V6O16·nH2O as a cathode material for lithium-ion batteries has been evaluated. The KVO nanobelts demonstrated a high discharge capacity of 260 mAh g-1, and long-term cyclic stability up to 100 cycles at 1 A g-1. The effect of the vanadium valence state and unusual construction of the nanobelts, composed of crystalline and amorphous domains arranged alternately were also discussed in this work. The ex-situ measurements of discharged electrode materials by XRD, MP-AES, XAS and XPS show that during the subsequent charge/discharge cycle the potassium in the K2V6O16·nH2O structure are replacing by lithium. The structural stability of the potassium hexavandate during cycling depends on the initial vanadium valence state on the sample surface and the presence of the "fringe free" domains in the K2V6O16·nH2O nanobelts.
ABSTRACT
In this work, Ba x Sr1-x Ti1-y Fe y O3-δ perovskite-based mixed conducting ceramics (for x = 0, 0.2, 0.5 and y = 0.1, 0.8) were synthesized and studied. The structural analysis based on the X-ray diffraction results showed significant changes in the unit cell volume and Fe(Ti)-O distance as a function of Ba content. The morphology of the synthesized samples studied by means of scanning electron microscopy has shown different microstructures for different contents of barium and iron. Electrochemical impedance spectroscopy studies of transport properties in a wide temperature range in the dry- and wet air confirmed the influence of barium cations on charge transport in the studied samples. The total conductivity values were in the range of 10-3 to 100 S cm-1 at 600 °C. Depending on the barium and iron content, the observed change of conductivity either increases or decreases in humidified air. Thermogravimetric measurements have shown the existence of proton defects in some of the analysed materials. The highest observed molar proton concentration, equal to 5.0 × 10-2 mol mol-1 at 300 °C, was obtained for Ba0.2Sr0.8Ti0.9Fe0.1O2.95. The relations between the structure, morphology and electrical conductivity were discussed.
ABSTRACT
Molten salt synthesis (MSS) is a simple method for the preparation of ceramic powders with specific morphology. The main role of the molten salts is to increase the reaction rate and lower the reaction temperature. It occurs because of much higher mobility of reactants in the liquid medium than in the solid state. In this work the molten salt synthesis was applied to produce ceramic powders of La0.995Ca0.005NbO4 and BaCe(0.9-x)Zr(x)Y0.1O3. Single-phase lanthanum niobate formed in all studied conditions of the synthesis, whereas in the case of barium cerate-zirconate MSS led to forming two crystalline phases: barium cerate and barium zirconate. The heating temperature and time as well as the salt content most strongly influenced the shape and size of particles. The influence of other parameters on the powder morphology was weaker. Despite differences in size and morphology, all groups of the La0.995Ca0.005NbO4 powder obtained with the MSS method pressed into pellets and sintered gave a dense ceramic material. On the other hand in the case of barium cerate-zirconate regardless of synthesis and sintering conditions the ceramics were porous.
