https://libjncir.jncasr.ac.in/xmlui/handle/10572/1478 2026-04-04T05:31:48Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2530 Tuning the Oxygen Release Temperature of Metal Peroxides over a Wide Range by Formation of Solid Solutions Lingampalli, S. R.; Dileep, K.; Datta, Ranjan; Gautam, Ujjal K. Metal peroxides, with a labile peroxy bond, constitute a distinct class of inorganic compounds that can generate singlet oxygen species and works as versatile reagents in many important industrial processes such as in polymer initiation reactions. Even after several decades after their discovery, the number of metal peroxides yet is few and their utility is severely limited by the corresponding decomposition temperatures (T-dec), which cannot be tuned to suit the most desirable condition for a particular reaction. One way of overcoming this would have been to obtain solid solutions of two peroxides with different decomposition temperatures. Surprisingly, in contrast to the vast majority of extended solids such as the oxide, hydroxide, and perovskite families, solid solutions of metal peroxides have remained so far nonexistent. Here, we explore and demonstrate that peroxides of Zn and Mg, ZnO2 (T-dec similar to 200 degrees C), and MgO2 (T-dec = 300 degrees C) can form solid solutions in the entire solubility range. Importantly, the decomposition temperatures of the solid solutions lie between that for the constituent phases and changes the composition systematically. These findings provide the first genuine chemical system that can potentially be tuned to decompose at different predesigned temperatures to generate reactive oxygen species. Restricted Access 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2499 Nanostructuring, carrier engineering and bond anharmonicity synergistically boost the thermoelectric performance of p-type AgSbSe2-ZnSe Guin, Satya N.; Negi, Devendra S.; Datta, Ranjan; Biswas, Kanishka Thermoelectric "waste heat-to-electrical energy" generation is an efficient and attractive option for robust and environmentally friendly renewable energy production. Simultaneous tailoring of interdependent thermoelectric parameters, i.e. electrical conductivity, thermopower and thermal conductivity, to improve the thermoelectric figure of merit is the utmost challenge in this field. Another important aspect is to develop high performance materials based on cheap and earth abundant materials. We have chosen AgSbSe2, a homologue of AgSbTe2 containing earth abundant selenium, as a model system for thermoelectric investigation due to its low thermal conductivity and favourable valence band structure. Herein, we show that by integrating different but synergistic concepts: (a) carrier engineering, (b) second phase endotaxial nanostructuring and (c) bond anharmonicity, we can achieve a maximum ZT of similar to 1.1 at 635 K in AgSbSe2-ZnSe (2 mol%), which is significantly higher than that of pristine AgSbSe2. The above system therefore offers promise to replace traditional metal tellurides for mid-temperature power generation. We demonstrate a design strategy which provides simultaneous enhancement of electrical transport through optimized doping, superior thermopower by the convergence of degenerate valence bands, and glass-like thermal conductivity due to the effective scattering of phonons by nanostructuring, bond anharmonicity and a disordered cation sublattice. Restricted Access 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2494 Direct evidence of strong local ferroelectric ordering in a thermoelectric semiconductor Aggarwal, Leena; Sekhon, Jagmeet S.; Guin, Satya N.; Arora, Ashima; Negi, Devendra S.; Datta, Ranjan; Biswas, Kanishka; Sheett, Goutam It is thought that the proposed new family of multi-functional materials, namely, the ferroelectric thermoelectrics may exhibit enhanced functionalities due to the coupling of the thermoelectric parameters with ferroelectric polarization in solids. Therefore, the ferroelectric thermoelectrics are expected to be of immense technological and fundamental significance. As a first step towards this direction, it is most important to identify the existing high performance thermoelectric materials exhibiting ferroelectricity. Herein, through the direct measurement of local polarization switching, we show that the recently discovered thermoelectric semiconductor AgSbSe2 has local ferroelectric ordering. Using piezo-response force microscopy, we demonstrate the existence of nanometer scale ferroelectric domains that can be switched by external electric field. These observations are intriguing as AgSbSe2 crystalizes in cubic rock-salt structure with centro-symmetric space group (Fm-3m), and therefore, no ferroelectricity is expected. However, from high resolution transmission electron microscopy measurement, we found the evidence of local superstructure formation which, we believe, leads to local distortion of the centro-symmetric arrangement in AgSbSe2 and gives rise to the observed ferroelectricity. Stereochemically active 5S(2) lone-pair of Sb may also give rise to local structural distortion thereby creating ferroelectricity in AgSbSe2. (C) 2014 AIP Publishing LLC. Restricted Access 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2466 Phase separation and electronic structure of ZnS0.3O0.7 alloy thin film with and without (Ag, Li) co-doping Dileep, K.; Datta, Ranjan ZnS0.3O0.7 alloy thin film with and without Ag and Li co-doping are grown by pulsed laser deposition on c-plane sapphire substrate. The films are phase separated in S-rich and S-poor regions. Two and four different phases are observed to form in (Ag, Li)(0.05):Zn0.95S0.3O0.7 and ZnS0.3O0.7 films respectively. Different phases and their relative volume fractions have been identified by electron diffraction pattern. The band gap corresponding to each phase is identified by low loss region of high resolution electron energy loss spectra. Band bowing parameter upon S doping is found to be 4.12 eV which closely match with Wien2k based density functional theory calculation utilizing mBJLDA exchange correlation potential. Oxygen positions have been replaced by sulphur in the lattice as confirmed by S L-3,L-2 electron energy loss near edge absorption spectra. High resolution electron energy loss spectroscopy has been used to collect core level spectra of various dopants in order to identify their locations in the lattice. Experimental Ag M-5,M-4 extended energy loss fine structure and Li K electron energy loss near edge structure in (Ag, Li): ZnS0.3O0.7 alloy have been compared with calculated spectra using FEFF code, suggesting that Ag and Li have taken up both the substitution and interstitial positions in the lattice. All the samples are resistive with resistance in the range of a few mega-ohms. (C) 2013 Elsevier B. V. All rights reserved. Restricted Access 2014-01-01T00:00:00Z