Browsing by Author "Satyam Kumar"

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Dielectric and photoconductivity dependence study of four-wave mixing process in photorefractive materials
(Springer, 2022) T.K. Yadav; M.K. Maurya; Satyam Kumar; R.A. Yadav
Phase-conjugate (PC) reflectivity is one of the most important parameters that characterize the four-wave mixing process in photorefractive (PR) materials. In this paper, the effect of the crystal thickness, modulation ratio and pump intensity ratio on the PC reflectivity of four-wave has been studied in case of the degenerate four-wave mixing process in PR materials. Also, the influence of photoconductivity and dielectric constant of PR materials on the PC reflectivity of the four-wave has been analyzed in case of the non-degenerate wave mixing process of PR materials. It has been found that the reflectivity of the PC wave for BGO and BSO have shown almost similar behavior like LiNbO3 with the peak values observed at 1.21 pS/cm and 1.69 pS/cm. The present results showed that the reflectivity of the PC wave is different for all the materials of dielectric constant 32 (LiNbO3), 40 (BGO) and 56 (BSO) and is higher for higher value of dielectric constant, suggesting that the reflectivity of the PC wave not only depends on the dielectric constant of the photorefractive materials but also strongly depends upon the photoconductivity of the materials. For lower value of coupling coefficient, it is observed that the peak intensity of reflectivity of PC wave occur at higher thickness and for higher values of coupling coefficient it is observed at lower crystal thickness. The enhancement in the reflectivity of the optical phase-conjugate wave would greatly improve the performance of the devices based on the four wave mixing process. Such devices find applications in the areas like optical memories, information processing, real-time processing, beam steering, beam combining, resonators and pattern formation. © 2021, Indian Association for the Cultivation of Science.
Particle size dependence on the structural, transport and optical properties of charge-ordered Pr0.6Ca0.4MnO3
(Elsevier Ltd, 2015) Satyam Kumar; G.D. Dwivedi; J. Lourembam; Shiv Kumar; U. Saxena; A.K. Ghosh; H. Chou; Sandip Chatterjee
Abstract Structural, transport and optical properties of nano-crystalline Pr0.6Ca0.4MnO3 have been investigated to emphasize on the semiconducting properties of charge-ordered manganite. Rietveld refinement of X-ray diffraction pattern of Pr0.6Ca0.4MnO3 nanoparticles show that due to increase in sintering temperature, MnO6 octahedra elongated along z-direction and compressed in x-y plane. Both Mn-O-Mn angles are found to decrease with increasing sintering temperature. Fourier transform infrared (FTIR) spectroscopy measurements reveal that the stretching and bending vibration of Mn-O-Mn is responsible for the change in Mn-O-Mn bond length and bond angle respectively. With increasing sintering temperature, these vibrations tend to increase, which resulted in the further distortion of MnO6 octahedra. Magnetic measurements suggest that charge ordering is established and system becomes antiferromagnetic with increasing particle size. Resistivity behavior of Pr0.6Ca0.4MnO3 nanoparticles clearly exhibit semiconducting nature of these systems, which is due to the formation of charge-ordered state of Mn3+ and Mn4+. Estimated optical band-gap of ∼3.7 eV for Pr0.6Ca0.4MnO3 nanocrystals, makes it a potential candidate for wide band-gap magnetic semiconductors. © 2015 Published by Elsevier B.V.
Phase and structural nanoarchitectonics of Ce-Doped Sr2SnO4 for improved microwave dielectric and electrical properties
(Springer Science and Business Media Deutschland GmbH, 2025) Upendra Kumar; Satyam Kumar; Abhishek Kumar Singh; Piyush Kumar Sonkar
To support the advancement of layered perovskite ceramics for next-generation wireless and millimeter-wave communication technologies, a series of Sr2Sn1−xCexO4 (x = 0, 0.10, 0.20, 0.30, 0.40, and 0.50) (SSC) were synthesized via the conventional solid-state reaction method, followed by calcination at 1100 °C and sintering at 1300 °C. Structural analysis through X-ray diffraction (XRD) confirmed the formation of a single-phase tetragonal crystal structure (space group I4/mmm) for compositions up to x = 0.20. Beyond this concentration, the emergence of a secondary Sr2CeO4 phase indicated a solubility limit for Ce substitution at the Sn site between x = 0.20 and x = 0.30. This structural evolution was further corroborated by FTIR and Raman spectroscopy, which supported the phase transition and changes in local bonding environments. Microstructural examinations revealed that Ce doping significantly influenced grain morphology and agglomeration tendencies. The coexistence of oxygen vacancies, interstitials, and multivalent cations—namely Sn2+/Sn4+ and Ce2+/Ce3+/Ce4+ played a crucial role in modulating the electrical and microwave dielectric behavior. Dielectric properties were predominantly governed by orientational polarization mechanisms linked to defect dipoles such as () and (). Electrical conduction followed an Arrhenius-type thermally activated process, dominated by doubly ionized oxygen vacancies and mixed ionic–electronic transport through electron exchange at Sn/Ce sites. The microwave dielectric response was primarily driven by electronic polarization, with optimal performance observed at x = 0.20 (ε = 12, Q×f = 23,482, =108 ppm/°C). The synergy between the enhanced electrical and dielectric characteristics underscores the potential of Ce-doped Sr₂SnO₄ (SSC) ceramics for application in intermediate-temperature solid oxide fuel cell (IT-SOFC) electrodes and millimeter-wave communication systems, offering a promising avenue for advanced multifunctional ceramic materials. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Structural, magnetic, magneto-transport properties, and electronic structure study of charge-ordered (La0.4Pr0.6)0.65Ca0.35MnO3
(Elsevier Ltd, 2017) G.D. Dwivedi; Satyam Kumar; Amish G. Joshi; Shiv Kumar; A.K. Ghosh; H. Chou; H.D. Yang; Sandip Chatterjee
Structural, magnetic and magneto-transport properties of nanocrystalline (La0.4Pr0.6)0.65Ca0.35MnO3have been investigated along with their electronic structures. Temperature dependent magnetization measurement shows different magnetic phases in different temperature regions. (La0.4Pr0.6)0.65Ca0.35MnO3completely transforms into a ferromagnet below 50 K. The temperature dependent resistivity measurement of (La0.4Pr0.6)0.65Ca0.35MnO3system displays semiconducting behavior up to 45 K under zero magnetic field. Application of 1 T magnetic field enforces semiconductor to metal transition around 65 K during cooling and around 115 K during warming. This shows that (La0.4Pr0.6)0.65Ca0.35MnO3still behaves as itinerant ferromagnet under applied magnetic field. X-ray photoemission spectra of Mn2p and Mn3s core-level confirm dual valence states of Mn (Mn3+and Mn4+), which is responsible for the magnetic behavior of the (La0.4Pr0.6)0.65Ca0.35MnO3system. High-resolution ultraviolet photoemission spectra near Fermi-edge confirms the presence of finite electronic states at Fermi-level, which explains the observed low-temperature metallic behavior of the (La0.4Pr0.6)0.65Ca0.35MnO3system. © 2016
Structural, transport and optical properties of (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals: A wide band-gap magnetic semiconductor
(Royal Society of Chemistry, 2015) Satyam Kumar; G.D. Dwivedi; Shiv Kumar; R.B. Mathur; U. Saxena; A.K. Ghosh; Amish G. Joshi; H.D. Yang; Sandip Chatterjee
(La0.6Pr0.4)0.65Ca0.35MnO3 system has been synthesized via a sol-gel route at different sintering temperatures. Structural, transport and optical measurements have been carried out to investigate (La0.6Pr0.4)0.65Ca0.35MnO3 nanoparticles. Raman spectra show that Jahn-Teller distortion has been decreased due to the presence of Ca and Pr in A-site. Magnetic measurements provide a Curie temperature around 200 K and saturation magnetization (MS) of about 3.43μB/Mn at 5 K. X-ray photoemission spectroscopy study suggests that Mn exists in a dual oxidation state (Mn3+ and Mn4+). Resistivity measurements suggest that charge-ordered states of Mn3+ and Mn4+, which might be influenced by the presence of Pr, have enhanced insulating behavior in (La0.6Pr0.4)0.65Ca0.35MnO3. Band gap estimated from UV-Vis spectroscopy measurements comes in the range of wide band gap semiconductors (∼3.5 eV); this makes (La0.6Pr0.4)0.65Ca0.35MnO3 a potential candidate for device application. This journal is © The Royal Society of Chemistry 2015.
Synthesis and investigation of structural, morphological and dielectric properties of Ba-ordered BaTiO3 perovskite oxide
(John Wiley and Sons Inc, 2024) Ram Sundar Maurya; Vedika Yadav; Harshpreet Cheema; Minakshi Sharma; P.A. Alvi; Satyam Kumar; Piyush Kumar Sonkar; Upendra Kumar
The samples with A-site cation ordering Ba1−x/2Ti1−xNbxO3 (BTN) with 0 ≤ x ≤ 0.010 were synthesized via the conventional ceramic route by calcining at 1200°C and sintered at 1350°C. The preliminary study of the phase of prepared samples was determined through X-ray diffraction (XRD) analysis. The Rietveld refinement analysis indicates the tetragonal phase in BTN0 sample, whereas the doped samples exhibit a combination of tetragonal and cubic phases. Presence of Raman band at 308 cm−1 suggests the presence of tetragonal in all samples. The dielectric constant was observed to be 1500 (BTN0), 3000 (BTN5) and 1680 (BTN10) while tangent loss found 0.6 (BTN0), 0.04 (BTN5) and 0.07 (BTN10). All the sample shows same Curie temperature (120°C) due to Ba-site cation ordering in the sample. Ferroelectric nature in all samples was also confirmed by modified Curie-Weis law. Based on the current studies, the present materials can be explored as a potential candidate for ferroelectric-memory devices, dielectric capacitor and energy harvesting applications. © 2023 John Wiley & Sons Ltd.