S. Bhattacharyya

Indian Institute of Management & Research, Jeypore, Rajasthan, India

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Publications (17)22.13 Total impact

  • Apurba Laha, S Bhattacharyya, S.B Krupanidhi
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    ABSTRACT: Relaxor thin films of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) with different microstructures have been grown on platinum-coated silicon substrate using pulsed excimer laser ablation technique. The microstructure of the thin films was found to be strongly influenced by the substrate temperature and the substrate microstructure. An intermediate layer of La0.5Sr0.5CoO3 (LSCO) was deposited on the platinum-coated silicon substrate prior to the deposition of the (PMN–PT) thin films. We found that the both the microstructure and perovskite phase in the PMN–PT thin films could be controlled by monitoring the substrate temperature along with the microstructure of the template layer. The dielectric properties of the films with different microstructure were studied as a function frequency over a wide range of temperatures. A direct impact of the microstructure on relaxor properties has been observed in the present case.
    Materials Science and Engineering B 01/2004; 106(2):111-119. · 1.85 Impact Factor
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    P. Victor, S. Bhattacharyya, S. B. Krupanidhi
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    ABSTRACT: Relaxation and conduction mechanisms under small ac fields of laser ablated ZrTiO4 thin films were analyzed in the light of impedance and modulus spectroscopy. The overall dielectric properties were mainly dominated by a Maxwell–Wagner type of relaxation with grains and the grain boundary two distinct parts of the circuit. Each of these parts was found to follow the universal power law of frequency dispersion. The modulus plot confirmed that the capacitive parts were relatively independent of the frequency and temperature, whereas the impedance and ac conduction studies exhibited significant temperature and frequency dependence. The conduction inside the grains was suggestive of a hopping mechanism through various defect sites whereas the interface barrier potential dictated grain boundary conduction. © 2003 American Institute of Physics.
    Journal of Applied Physics 10/2003; 94(8):5135-5142. · 2.21 Impact Factor
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    S. Bhattacharyya, Apurba Laha, S. B. Krupanidhi
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    ABSTRACT: The ferroelectric properties of SrBi2Ta2O9 thin films grown by laser ablation were investigated as a function of the Sr+2 content in the films. Different target compositions were used to obtain films with different Sr+2/Ta+5 ratios. The initial composition was according to the stoichiometric composition (1/2), and the Sr+2/Ta+5 ratio was varied to 0.7/2.0. It was seen that the remanent polarization showed a consistent increase, as the film became more deficient of “Sr+2” up to a certain extent. Similarly, a decrease in the dielectric constant and the leakage current with the decrease of Sr+2 in the film was observed. The dielectric transition temperature showed an increase with the reduction of Sr+2 content and was seen to approach the bulk value. © 2002 American Institute of Physics.
    Journal of Applied Physics 07/2002; 92(2):1056-1061. · 2.21 Impact Factor
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    ABSTRACT: Lead zirconate is a room temperature antiferroelectric material, which exhibits double polarization hysteresis characteristic in the presence of external field. A transformation from antiferroelectric to paraelectric behavior through a ferroelectric phase has been exhibited upon addition of La-to pure lead zirconate thin films, which were confirmed from dielectric, hysteresis and pyroelectric and micro Raman analyses. Thin films of pure and La-modified lead zirconate were processed using A-site vacancy formula Pb(l−1.5x)LaXZrO3 by pulsed excimer laser ablation technique. Pyroelectric coefficient increased gradually from 55 to 190 μC cm−2 K−1 with the addition of 0 to 9 mole% of La to pure lead zirconate. The transition temperature has been reduced to room temperature (∼34 °C) with addition of a 9 mole% of La-to lead zirconate. Presence of antiferroelectricity in pure lead zirconate thin films is due to antiparallel shifts of Pb-ions in (110) direction and reduction of transition temperature is attributed to creation of A-site vacancies would have caused enhancing of ferro-and paraelectric behavior with La-addition.
    Thin Solid Films 01/2002; 88(1):22–25. · 1.87 Impact Factor
  • S. Bhattacharyya, Apurba Laha, S. B. Krupanidhi
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    ABSTRACT: The dc conduction behavior of thin films of SrBi2Ta2O9 (SBT) has been investigated on the basis of space-charge limited current theory. The theory was generalized to account for the traps, which were inevitably present in this case. The relative percentage of trapped injected charge and the free injected charge was seen to follow a dynamical equilibrium instead of the true thermal equilibrium as the temperature of the sample was raised during the measurement. The onset voltage of the trap filled region (VTFL) showed a decreasing trend with the increase of temperature. This reduction of VTFL was ascribed to the appearance of some excess charge in the conduction band. It was seen that the thermodynamically stable distribution of charges among the energy levels could not be taken to explain such a situation. A dynamic model was proposed to explain this kind of a nonequilibrium distribution of trapped and free charges.
    Journal of Applied Physics 01/2002; 91:4543-4548. · 2.21 Impact Factor
  • Sandip Halder, Sudipta Bhattacharyya, S. B Krupanidhi
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    ABSTRACT: In situ annealed thin films of ferroelectric Ba(Zr0.1Ti0.9)O3 were deposited on platinum substrates by pulsed laser ablation technique. The as grown films were polycrystalline in nature without the evidence of any secondary phases. The polarization hysteresis loop confirmed the ferroelectricity, which was also cross-checked with the capacitance–voltage characteristics. The remnant polarization was about 5.9 μC cm−2 at room temperature and the coercive field was 45 kV. There was a slight asymmetry in the hysteresis for different polarities, which was thought to be due to the work function differences of different electrodes. The dielectric constant was about 452 and was found to exhibit low frequency dispersion that increased with frequency. This was related to the space-charge polarization. The complex impedance was plotted and this exhibited a semicircular trace, and indicated an equivalent parallel R–C circuit within the sample. This was attributed to the grain response. The DC leakage current–voltage plot was consistent with the space-charge limited conduction theory, but showed some deviation, which was explained by assuming a Poole–Frenkel type conduction to be superimposed on to the usual space-charge controlled current.
    Materials Science and Engineering B-advanced Functional Solid-state Materials. 01/2002; 95(2):124-130.
  • S. Bhattacharyya, S Saha, S. B Krupanidhi
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    ABSTRACT: The reversible and irreversible components of the total polarization in a thin film of SrBi2(Ta0.5,Nb0.5)2O9 were calculated. The C–V loop was integrated to obtain the reversible part of the total polarization. The reversible polarization was only 20% of the total polarization and showed almost no hysteresis. However, the dielectric constant due to the total polarization was almost the same as that for the reversible polarization in the saturation region of the large signal P–E hysteresis loop. The reversible part was subtracted from the total polarization to calculate the irreversible counterpart of it. The irreversible polarization showed a near-square shaped hysteresis loop, while the reversible polarization was obeying the Rayleigh law. The small signal hysteresis was simulated from the parameters obtained from the Rayleigh-curve fit with the experimental curve and then it was compared with the result obtained from direct measurement with small amplitude.
    Thin Solid Films 01/2002; 422(1):155-160. · 1.87 Impact Factor
  • S. Bhattacharyya, P. Victor, A. Laha, S. B. Krupanidhi
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    ABSTRACT: The thickness dependence of the electrical properties in the thin films of uniaxial SrBi 2 Nb 2 O 9 has been studied in this report. According to many published literatures, it could be an effective way to identify the basic conduction process. The laser ablation was chosen as the deposition technique to ensure an oriented growth and a proper stoichiometric deposition. The structural, dielectric and conduction properties were studied as a function of thickness. The films showed good ferroelectric properties, an ordered growth, and a space-charge controlled conduction process, which was double checked by reversing the polarity of the applied voltage, and also by examining the high field current response of the sample varying in thickness.
    Integrated Ferroelectrics 01/2002; 50(1):159-169. · 0.38 Impact Factor
  • P. Victor, S. Bhattacharyya, S. Saha, S. B. Krupanidhi
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    ABSTRACT: Recently there is an increasing demand and extensive research on high density memories, in particular to the ferroelectric random access memory composed of 1T/1C (1 transistor/1 capacitor) or 2T/2C. FRAM's exhibit fast random acess in read/write mode, non - volatility and low power for good performance. An integration of the ferroelectric on Si is the key importance and in this regard, there had been various models proposed like MFS, MFIS, MFMIS structure etc., Choosing the proper insulator is very essential for the better performance of the device and to exhibit excellent electrical characteristics. ZrTiO4 is a potential candidate because of its excellent thermal stability and lattice match on the Si substrate. SrBi2Ta2O9 and ZrTiO4 thin films were prepared on p - type Si substrate by pulsed excimer laser ablation technique. Optimization of both ZT and SBT thin films in MFS and MFIS structure had been done based on the annealing, oxygen partial pressures and substrate temperatures to have proper texture of the thin films. The dc leakage current, P - E hysteresis, capacitance - voltage and conductance - voltage measurement were carried out. The effect of the frequency dependence on MFIS structure was observed in the C – V curve. It displays a transition of C - V curve from high frequency to low frequency curve on subjection to varied frequencies. Density of interface states has been calculated using Terman and high - low frequency C - V curve. The effect of memory window in the C - V hysteresis were analysed in terms of film thickness and annealing temperatures. DC conduction mechanism were analysed in terms of poole - frenkel, Schottky and space charge limited conduction separately on MFS, MIS structure.
    MRS Online Proceeding Library 12/2001; 747.
  • S. Bhattacharyya, S. B. Krupanidhi
    Ferroelectrics. 01/2001; 260(1-4):161-167.
  • S. Bhattacharyya, S. B. Krupanidhi
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    ABSTRACT: Thin films of SrBi2Nb2O9 (SBN) were grown using pulsed laser ablation. A low substrate temperature deposition was chosen to ensure good film substrate interface, and hence good ferroelectric property. A nearly polycrystalline structure was achieved after ex-situ annealing. The lower switching voltage was obtained by lowering the thickness, which did not affect the insulating nature of thefilm at all. The hysteresis results showed an excellent square shaped loop with Pr=15 μC/cm and Ec = 75 kV/cm respectively. The response of the film to external ac stimuli was studied at different temperatures, and it showed that ac conductivity values in the limiting case are in close agreement with dc values, and correspond to oxygen vacancy motion.
    Integrated Ferroelectrics 01/2001; 32(1-4):101-119. · 0.38 Impact Factor
  • Integrated Ferroelectrics 11/2000; 31(1-4):1-12. · 0.38 Impact Factor
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    ABSTRACT: Bi-layered Aurivillius compounds prove to be efficient candidates of nonvolatile memories. SrBi2Nb2O9 thin films were deposited by excimer laser ablation at low substrate temperature (400 °C) followed by an ex situ annealing at 750 °C. The polarization hysteresis behavior was confirmed by variation of polarization with the external applied electric field and also verified with capacitance versus voltage characteristics. The measured values of spontaneous and remnant polarizations were, respectively, 9 and 6 μC/cm2 with a coercive field of 90 kV/cm. The measured dielectric constant and dissipation factors at 100 kHz were 220 and 0.02, respectively. The frequency analysis of dielectric and ac conduction properties showed a distribution of relaxation times due to the presence of multiple grain boundaries in the films. The values of activation energies from the dissipation factor and grain interior resistance were found to be 0.9 and 1.3 eV, respectively. The deviation in these values was attributed to the energetic conditions of the grain boundaries and bulk grains. The macroscopic relaxation phenomenon is controlled by the higher resistive component in a film, such as grain boundaries at lower temperatures, which was highlighted in the present article in close relation to interior grain relaxation and conduction properties. © 2000 American Institute of Physics.
    Journal of Applied Physics 09/2000; 88(7):4294-4302. · 2.21 Impact Factor
  • S. Bhattacharyya, S. S. N Bharadwaja, S. B Krupanidhi
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    ABSTRACT: Thin films of SrBi2(Ta,Nb)2O9 (SBTN) were grown using pulsed-laser ablation and were ex situ crystallized. Ferroelectric properties were achieved by low temperature deposition. A polycrystalline structure was achieved, with a Ta- to Nb-ratio nearly 1:1. The smaller thickness of the film allowed the switching voltage to be low enough (1.5V), without affecting the insulating nature of the films. The hysteresis results showed an excellent square shaped loop with a remnant polarization (Pr) of 7.6μC/cm2 and a coercive field (Ec) of 75kV/cm. This ferroelectric material composition is having a very high Curie temperature with higher stability and can be used in non-volatile random access memory (NVRAM) devices.
    Solid State Communications 01/2000; 114(11):585-588. · 1.53 Impact Factor
  • S. Bhattacharyya, S. B. Krupanidhi
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    ABSTRACT: Ex-situ grown thin films of SrBi2Nb2O9 (SBN) were deposited on platinum substrates using laser ablation technique. A low substrate-temperature-processing route was chosen to avoid any diffusion of bismuth into the Pt electrode. It was observed that the as grown films showed an oriented growth along the ′c′-axis (with zero spontaneous polarization). The as grown films were subsequently annealed to enhance crystallization. Upon annealing, these films transformed into a polycrystalline structure, and exhibited excellent ferroelectric properties. The switching was made to be possible by lowering the thickness without losing the electrically insulating behavior of the films. The hysteresis results showed an excellent square-shaped loop with results (Pr = 4 uC/cm; Ec = 90 kV/cm) in good agreement with the earlier reports. The films also exhibited a dielectric constant of 190 and a dissipation factor of 0.02, which showed dispersion at low frequencies. The frequency dispersion was found to obey Jonscher's universal power law relation, and was attributed to the ionic charge hopping process according to earlier reports. The dc transport studies indicated an ohmic behavior in the low voltage region, while higher voltages induced a bulk space charge and resulted in non-linear current-voltage dependence.
    Integrated Ferroelectrics - INTEGR FERROELECTRICS. 01/2000; 31:57-67.
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    ABSTRACT: Polycrystalline films of SrBi2Nb2O9 were grown using pulsed-laser ablation. The ferroelectric properties were achieved by low-temperature deposition followed by a subsequent annealing process. The lower switching voltage was obtained by lowering the thickness, which did not affect the insulating nature of the films. The hysteresis results showed an excellent square-shaped loop with results (Pr = 6 μC/cm2, Ec = 100 kV/cm) in good agreement with earlier reports. The films also exhibited a dielectric constant of 250 and a dissipation factor of 0.02. The transport studies indicated an ohmic behavior, while higher voltages induced a bulk space charge. © 1999 American Institute of Physics.
    Applied Physics Letters 10/1999; 75(17):2656-2658. · 3.52 Impact Factor
  • S. Bhattacharyya, A. R James, S. B Krupanidhi
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    ABSTRACT: Ex-situ and in-situ crystallised films of SrBi2Ta2O9 (SBT) were grown using pulsed laser ablation. Different growth parameters were used for ablation. Both low temperature grown films, followed by annealing and high temperature grown ones were used for comparison. It was found that in-situ crystallised films showed better electrical properties over the annealed films, vis-à-vis the hysteresis loops and dielectric constants. It was also observed that the Bi concentration (which was estimated by EDS analysis) had a marked influence on the ferroelectric properties. With stoichiometric or excess Bi content, growth of in-situ crystallised films resulted in the observation of square hysteresis loops with a Pr value of 10μC/cm2 and a coercive field of 24kV/cm, which appears very attractive for NVRAM applications.
    Solid State Communications 01/1998; 108(10):759-763. · 1.53 Impact Factor