Department Of Physics

Permanent URI for this communityhttps://kr.cup.edu.in/handle/32116/57

Browse

Author: search.filters.author.Prakash, Jai

Search Results

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    Tunable dielectric and memory features of ferroelectric layered perovskite Bi4Ti3O12 nanoparticles doped nematic liquid crystal composite
    (Elsevier B.V., 2022-11-24T00:00:00) Anu; Varshney, Depanshu; Yadav, Kamlesh; Prakash, Jai; Meena, Harikesh; Singh, Gautam
    Herein, we report the synthesis of ferroelectric layered perovskite Bi4Ti3O12 (BT4) nanoparticles (NPs) and the temperature-dependent dielectric and electro-optical (especially memory effect) properties of 4-pentyl-4?-cyanobiphenyl (5CB) nematic liquid crystal (NLC) doped with 1 wt% BT4 NPs (i.e. 5CB-BT4 composite) using polarising optical microscopy and frequency-dependent dielectric spectroscopy techniques. BT4 NPs were synthesised via a microwave-assisted chemical method and characterised using various instrumental techniques, which confirmed the formation of a non-stoichiometric and oxygen-deficient orthorhombic crystal phase. The agglomeration-free and uniform dispersion of BT4 NPs in the 5CB matrix was confirmed by optical textures. The optical memory studied by bias voltage-dependent (ON-OFF) optical textures is decreased by ? 2.6 times in the 5CB-BT4 composite compared with 5CB. Moreover, dielectric parameters such as dielectric permittivity, dielectric loss, loss tangent, conductivity, and activation energy of 5CB and composite (5CB-BT4) are estimated using dielectric spectroscopy. The dielectric anisotropy is decreased, whereas no shift in the clearing temperature is observed in the 5CB-BT4 composite compared to the 5CB sample. Also, the DC conductivity of 5CB-BT4 composite is found to be increased by approximately four times compared to the 5CB. Our studies clearly demonstrate the tunability of the dielectric and optical memory features of NLC (5CB) matrix by dopant BT4 NPs, without significantly affecting the molecular alignment of the NLC molecules. Such composites would certainly be useful in the fabrication of NLC based tunable devices such as optical memory and conductivity switches. � 2022 Elsevier B.V.
  • No Thumbnail Available
    Item
    Probing the impact of bismuth-titanate based nanocomposite on the dielectric and electro-optical features of a nematic liquid crystal material
    (Elsevier B.V., 2021-12-22T00:00:00) Varshney, Depanshu; Anu; Prakash, Jai; Pratap Singh, Vinay; Yadav, Kamlesh; Singh, Gautam
    We report here the concentration and temperature dependent optical, electro-optical and dielectric studies on bismuth titanate (Bi2Ti2O7/Bi4Ti3O12) nanocomposite (BT2/BT4 NC, ?42 nm) doped nematic liquid crystal (NLC, 5CB) mixtures using optical polarising microscope and dielectric spectroscopic techniques. The optical textures confirm the uniform dispersion and miscibility of NCs in 5CB for all concentrations (i.e. 0.1, 0.25, 0.5, 1 and 2 wt%) and mixtures appear to be almost agglomeration free. The dielectric studies demonstrate the maximum changes in the dielectric parameters (dielectric permittivity, dielectric loss, loss factor and dielectric anisotropy) of 5CB sample for the 0.1 wt% mixture. Interestingly, the dielectric anisotropy of 5CB in 0.1 wt% mixture is increased by ? 11%. However, the dielectric memory effect (bias voltage ON-OFF) is observed maximum in the case of 1 wt% mixture. Similarly, the optical memory examined by bias voltage dependent (ON-OFF) optical textures is also significantly enhanced for 1 wt% mixture. The significant changes observed in dielectric properties of 5CB sample could be due to plausible interaction among NLC molecules and ionic impurities with BT2/BT4 NCs. Moreover, the enhanced volatile memory in BT2/BT4 NC-NLC mixture could be attributed to the dipole�dipole coupling between individual permanent dipole moment of anisotropic NLC molecules with the dipole moments generated by the ionic impurities agglomerated on the surface of high dielectric BT2/BT4 NCs. We strongly believe that such NCs-NLC mixtures would be certainly useful in the advancement of wearable devices (such as smart plenoptic cameras, watches etc.) and smart switchable windows. � 2021 Elsevier B.V.
  • Thumbnail Image
    Item
    Probing the effect of temperature and electric field on the low frequency dielectric relaxation in a ferroelectric liquid crystal mesogen
    (Elsevier, 2014) Chandran, Achu; Prakash, Jai; Joshi, Tilak; Biradar, A. M.
    We present the characterization and dielectric spectroscopic investigations of a ferroelectric liquid crystal (FLC) material, namely KCFLC 10S. We experimentally demonstrate the observation of a low frequency dielectric relaxation mode along with Goldstone mode in the smectic C* phase of the FLC material under investigation. The behavior of low frequency dielectric relaxation mode has been systematically studied with temperature and applied bias field. The relaxation frequency of the low frequency dielectric relaxation has been found to be shifted toward the higher frequency side with an increase in temperature and field strength. This shift has been attributed to the single particle diffusion of fast ions. Further investigations on electrical conductivity (σ) with frequency at different electric field strengths revealed a Schottky-type of charge injection at electrode even under a small DC bias. The studies carried out in the present paper would be helpful to provide ideas for designing and developing advanced liquid crystal materials.
  • Thumbnail Image
    Item
    Preparation and characterization of MgO nanoparticles/ferroelectric liquid crystal composites for faster display devices with improved contrast
    (2014) Chandran, Achu; Prakash, Jai; Naik, Kush Kumar; Srivastava, Avanish; Dabrowski, Roma; Czerwinki, Michat; Biradar, A. M.; Chandran, A.; Prakash, J.; Naik, K.K.; Srivastava, A.K.; Da?browski, R.; Czerwi?ski, M.; Biradar, A.M.
    In this article, we present the formulation and characterization of a ferroelectric liquid crystal (FLC) mixture W301 composed of pyrimidine compounds. We observed that upon doping magnesium oxide nanoparticles (MgO NPs) into the host FLC, the MgO NPs/FLC composite showed significantly faster response and improved optical tilt angle. The decreased response time in the MgO NPs/FLC composite has been attributed to the decrease in rotational viscosity and increase in surface anchoring energy. The decrease in rotational viscosity of the composite is due to the torque experienced by both MgO NPs and FLC in the presence of an electric field and perturbations of order parameters of FLC. Due to the enhanced surface interaction of MgO NPs having surface defects with mesogens, strong surface anchoring is experienced on the FLC molecules that not only increased the speed of the response but also improved the optical tilt angle of the MgO NPs/FLC composites, which ultimately resulted in improved contrast. A systematic approach has been followed to elucidate the idea of designing faster display devices with improved contrast based on MgO NPs/FLC composites. ? 2014 The Royal Society of Chemistry.