Insulator to metal (IMT) transition (Tt ∼ 341 K) in the VO2 accompanies transition from an infrared (IR) transparent to IR opaque phase. Tailoring of the IMT and associated IR switching behavior can offer potential thermochromic applications. Here we report on effects of the W and the Tb doping on the IMT and associated structural, electronic structure and optical properties of the VO2 thin film. Our results show that the W doping significantly lowers IMT temperature (∼ 292 K to ∼ 247 K for 1.3% W to 3.7% W) by stabilizing the metallic rutile, R, phase while Tb doping does not alter the IMT temperature much and retains the insulating monoclinic, M1 , phase at room temperature. It is observed that the W doping albeit significantly reduces the IR switching temperature but is detrimental to the solar modulation ability, contrary to the Tb doping effects where higher IR switching temperature and solar modulation ability is observed. The IMT behavior, electrical conductivity and IR switching behavior in the W and the Tb doped thin films are found to be directly associated with the spectral changes in the V 3d states.
Thermal conductivity, which measures the ease at which heat passes through a crystalline solid, is controlled by the nature of the chemical bonding and periodicity in the solid. This necessitates an in‐depth understanding of the crystal structure and chemical bonding to tailor materials with notable lattice thermal conductivity (κL). Herein, the nature of chemical bonding and its influence on the thermal transport properties (2–523 K) of all‐inorganic halide perovskite Cs3Bi2I9 are studied. The κL exhibits an ultralow value of ≈0.20 W m−1K−1 in 30–523 K temperature range. The antibonding states just below the Fermi level in the electronic structure arising from the interaction between bismuth 6s and iodine 5p orbitals, weakens the bond and causes soft elasticity in Cs3Bi2I9. First‐principles density functional theory (DFT) calculations reveal highly localized soft optical phonon modes originating from Cs‐rattling and dynamic double octahedral distortion of 0D [Bi2I9]3− in Cs3Bi2I9. These low energy nearly flat optical phonons strongly interact with transverse acoustic modes creating an ultrashort phonon lifetime of ≈1 ps. While the presence of extended antibonding states gives rise to soft anharmonic lattice; Cs rattling provides sharp localized optical phonon modes, which altogether result in strong lattice anharmonicity and ultralow κL.
Woven jute fabric was used as a reinforcing material for making two types of composite, named Jute/PR and Jute/Epoxy, with two different matrixes of polyester resin and epoxy, respectively, by hand layup techniques. Five different doses of gamma radiation from 100 to 500 krad were used to investigate the effects of the mechanical properties of the composites and the jute fabrics. Though gamma radiation improved the mechanical properties, such as the tensile strength (TS) and Young’s modulus (Y), and decreased the elongation at break % (Eb%) of the composites, it deteriorated all these properties for jute fabrics. The highest values of TS and Y and the lowest value of Eb% were found to be 39.44 Mpa, 1218.33 Mpa, and 7.68% for the Jute/PR; and 48.83 Mpa, 1459.67 Mpa, and 3.68% for the Jute/Epoxy composites, respectively, at a 300 krad gamma radiation dose. A further increase in dose altered all these properties; thus, 300 krad was found to be the optimum dose for both of the composites. Between the two composites, gamma radiation influenced the Jute/PR composite more than the Jute/Epoxy composite.
Four types of nonwovens were prepared from different sections of the banana tree e.g., outer bark (OB), middle bark (MB), inner bark (IB) and midrib of leaf (MR) by wet laid web formation. They were reinforced with two different types of matrices e.g., epoxy and polyester, to make eight variants of composites. Treatments including alkali on raw fibers, water repellent on nonwovens and gamma radiation on composites were applied in order to investigate their effects on properties of the composites such as water absorbency, tensile strength (TS), flexural strength (FS) and elongation at break (Eb%). Variations in the morphological structure and chemical composition of both raw banana fibers and fibers reinforced by the treatments were analyzed by Fourier Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM). OB composites exhibited higher water absorbency, TS and FS and lower Eb% compared to other types of composites. Epoxy composites were found to have 16% lower water absorbency, 41.2% higher TS and 39.1% higher FS than polyester composites on an average. Water absorbency of the composites was reduced 32% by the alkali treatment and a further 63% by water repellent treatment. TS and FS of the composites were on average improved 71% and 87% by alkali treatment and a further 30% and 35% by gamma radiation respectively.
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