Browsing by Author "Acharya, A."

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    High Thermoelectric Figure of Merit (zT) in ?-Ag2Se via Aliovalent Doping
    (John Wiley and Sons Inc, 2025) Acharya, A.; Nagaraja, S.; Hassan, N.; Tarafder, K.; Ballav, N.
    High-performance thermoelectric materials are essential for efficient low-temperature (300–400 K) heat energy harvesting, with n-type Ag2Se being a promising candidate. To further enhance the thermoelectric figure of merit (zT) of Ag2Se, aliovalent doping has emerged as a key strategy. However, achieving wet-chemical aliovalent doping of Ag2Se at ambient temperature has proven challenging. In this work, a high zTmax of 1.57 at 398 K is reported for an optimally Cd(II)-doped Ag2Se sample, specifically in the structurally phase-pure Ag1.98Cd0.02Se, which is successfully synthesized via an aqueous-based method at room-temperature (300 K). The Ag1.98Cd0.02Se sample also exhibits an impressive average zTavg of 1.12 over the temperature range of 315–400 K. Density functional theory (DFT) calculations for both the pristine and doped samples reveal significant changes in the electronic band structures, including notable modulations in the density of states near the Fermi energy, particularly for the Ag-3d states. The remarkable thermoelectric performance of Ag1.98Cd0.02Se is attributed to an optimization of charge carrier induced by the Cd(II)-doping. © 2025 Wiley-VCH GmbH.
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    Thermally-driven conformational twist in organic azobenzene linker activates molecular doping effect in thin films of lanthanide MOFs
    (Royal Society of Chemistry, 2025) Bhoi, U.; Kalyani, M.; Ananthram, K.S.; Saha, S.; Acharya, A.; Hassan, N.; Raj, M.; Tarafder, K.; Ballav, N.
    Azobenzene-based photo-switchable molecules have shown significant potential in stimuli-responsive systems, especially when incorporated into metal–organic frameworks (MOFs). This study reports thin films of lanthanide-based metal–organic frameworks (Ln-MOFs) with 4,4?-azobenzene dicarboxylic acid (H2ADA) as the organic linker – Tb-ADA, Eu-ADA, and Gd-ADA – using an electrodeposition method. Upon heating to 400 K, a reversible structural transition was observed via variable temperature grazing-incidence X-ray diffraction (GIXRD) and Raman spectroscopy, not due to trans–cis isomerization but rather a thermally-induced conformational twist of the ADA linker. Density functional theory (DFT) combined with molecular dynamics (MD) simulations supports this interpretation, revealing high-energy atropisomeric states stabilized by MOF confinement. Molecular doping of these films with 7,7,8,8-tetracyanoquinodimethane (TCNQ) significantly enhanced their electrical conductivity, increasing by two orders of magnitude at 400 K. This enhancement is attributed to improved ?–? stacking and charge-transfer interactions facilitated by the conformational twist. Temperature-dependent X-ray photoelectron spectroscopy (XPS) confirmed redox activity in TCNQ@Tb-ADA films, showing reversible conversion between Tb(iii) and Tb(iv), with back electron transfer at 400 K restoring Tb(iii). These findings introduce a new mechanism of thermally-driven conformational switching in MOFs and open avenues for developing responsive electronic materials based on azobenzene linkers. This journal is © The Royal Society of Chemistry, 2025