Department Of Physics

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Author: search.filters.author.AnuSubject: search.filters.subject.Ferroelectric

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    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.
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    Effect of oxygen vacancies, lattice distortions and secondary phase on the structural, optical, dielectric and ferroelectric properties in Cd-doped Bi2Ti2O7 nanoparticles
    (Elsevier Ltd, 2021-04-27T00:00:00) Anu; Yadav, Kamlesh; Gaur, Anurag; Haldar, Krishna Kanta
    (Bi1-xCdx)2Ti2O7 (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10 and 0.12) nanoparticles are synthesised using the co-precipitation method. The prepared samples show pyrochlore phase formation except for x = 0.02 and 0.08, where Bi4Ti3O12 appears as a secondary phase. The crystallite size and unit cell volume decrease while the strain and dislocation density increase with an increase in Cd-doping. The vibrational bands corresponding to Cd?O and C[dbnd]O are red-shifted, while the H[sbnd]O[sbnd]H bending band is blue-shifted with increasing Cd-doping. The band gap energy for x = 0.00 is found to be 1.78 eV. It increases with an increase in �x� up to 0.06 and then decreases with a further increase in �x� except for x = 0.02 and x = 0.08. The impedance data show non-Debye type relaxation. The pyrochlore phase is found to be non-ferroelectric. However, the samples with x = 0.02 and x = 0.08 having the secondary phase (Bi4Ti3O12) are ferroelectric. � 2021 Elsevier Ltd