Halide ion (Cl−/Br−/I−) aliovalently dopes on the Se2−sublattice and contributes one n-type carrier in AgBiSe2, which gives rise to improved electronic transport properties. A peakZT, value of ∼0.9 at ∼810 K has been achieved for the AgBiSe1.98Cl0.02sample, which makes it a promising n-type thermoelectric material for mid-temperature applications.

We report here results based on electrochemical K-alloying/de-alloying and associated in-situ studies with Sn in K ‘half cells’. The as-recorded reversible K-capacity of ∼245 mAh/g agree with the ‘final’ phase (K4Sn4) observed in in-situ synchrotron XRD scans at the end of one K-alloying half cycle. The electrochemical cycling and in-situ XRD results indicate that K4Sn4 forms via one-step phase transformation with no prior Sn-K solid solution formation and reverts back to β-Sn after de-potassiation half cycle (leading to ∼85 ± 6% first cycle coulombic efficiency). Interestingly, no notable evidence for occurrence of irreversible surface reaction could be found during the 1st discharge. However, strong evidences for the same were recorded (at ∼1.3–1.4 V, against K/K+) after completion of one full K-alloying/de-alloying cycle. In-situ monitoring of stress developments in the Sn film electrodes during galvanostatic cycling indicated the occurrence of mechanical instability not only during K-alloying/de-alloying induced phase transformations, but also upon occurrence of the surface reactions (as supported by SEM observations), which also lead to development of compressive stresses by itself. Accordingly, galvanostatic cycling within restricted cell voltage window of 1.2–0.01 V, as against 2–0.01 V, suppressed the irreversible surface phenomena and improved the cyclic stability.

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Abstract:We present the results of Synchrotron XRD measurements on powdered single crystal samples of BaFe2-xRuxAs2, as a function of Ru content, and as a function of temperature, across the spin density wave transition in BaFe1.9Ru0.1As2. The Rietveld refinements reveal that with Ru substitution, while the a-axis increases, the c-axis decreases. In addition the variation of positional co-ordinates of As (zAs), the Fe-As bond length and the As-Fe-As bond angles have also been determined. In the sample with x=0.1, temperature dependent XRD measurements, indicate that the orthorhombicity shows the characteristic increase with decrease in temperature, below the magnetic transition. It is seen that the c-axis, the As-FeAs bond angles, Fe-As bond length and positional co-ordinate of the As show definite anomalies close to the structural transition. The observed anomalies in structural parameters are analysed in conjunction with geometric optimization of the structure using ab-initio electronic structure calculations.