Browsing by Author "Maurya, Deepam"

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    3D printed graphene-based self-powered strain sensors for smart tires in autonomous vehicles
    Maurya, Deepam; Khaleghian, Seyedmeysam; Sriramdas, Rammohan; Kumar, Prashant; Kishore, Ravi Anant; Kang, Min-Gyu; Kumar, Vireshwar; Song, Hyun-Cheol; Lee, Seul-Yi; Yan, Yongke; Park, Jung-Min (Jerry); Taheri, Saied; Priya, Shashank (2020-10-26)
    The transition of autonomous vehicles into fleets requires an advanced control system design that relies on continuous feedback from the tires. Smart tires enable continuous monitoring of dynamic parameters by combining strain sensing with traditional tire functions. Here, we provide breakthrough in this direction by demonstrating tire-integrated system that combines direct mask-less 3D printed strain gauges, flexible piezoelectric energy harvester for powering the sensors and secure wireless data transfer electronics, and machine learning for predictive data analysis. Ink of graphene based material was designed to directly print strain sensor for measuring tire-road interactions under varying driving speeds, normal load, and tire pressure. A secure wireless data transfer hardware powered by a piezoelectric patch is implemented to demonstrate self-powered sensing and wireless communication capability. Combined, this study significantly advances the design and fabrication of cost-effective smart tires by demonstrating practical self-powered wireless strain sensing capability. Designing efficient sensors for smart tires for autonomous vehicles remains a challenge. Here, the authors present a tire-integrated system that combines direct mask-less 3D printed strain gauges, flexible piezoelectric energy harvester for powering the sensors and secure wireless data transfer electronics, and machine learning for predictive data analysis.
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    Alternating and direct current field effects on the structure-property relationships in Na0.5Bi0.5TiO3-x% BaTiO3 textured ceramics
    Ge, Wenwei; Maurya, Deepam; Li, Jiefang; Priya, Shashank; Viehland, Dwight D. (AIP Publishing, 2013-06-01)
    The influence of alternating (ac) and direct current (dc) fields on the structural and dielectric properties of [001](PC) textured Na0.5Bi0.5TiO3-7%BaTiO3 (NBT-7%BT) ceramics has been investigated. X-ray diffraction measurements revealed that the depolarization at temperature T-d in poled samples resulted from a tetragonal -> pseudo-cubic transition on heating. Moderate ac drive and dc bias had opposite influences on T-d: ac drive decreased the T-d, whereas dc bias increased it. These investigations suggested an effective method to expand the working temperature range of NBT-x%BT textured ceramics to a high temperature. (C) 2013 AIP Publishing LLC.
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    Compositionally Graded Multilayer Ceramic Capacitors
    Song, Hyun-Cheol; Zhou, Jie E.; Maurya, Deepam; Yan, Yongke; Wang, Yu U.; Priya, Shashank (Springer Nature, 2017-09-27)
    Multilayer ceramic capacitors (MLCC) are widely used in consumer electronics. Here, we provide a transformative method for achieving high dielectric response and tunability over a wide temperature range through design of compositionally graded multilayer (CGML) architecture. Compositionally graded MLCCs were found to exhibit enhanced dielectric tunability (70%) along with small dielectric losses (< 2.5%) over the required temperature ranges specified in the standard industrial classifications. The compositional grading resulted in generation of internal bias field which enhanced the tunability due to increased nonlinearity. The electric field tunability of MLCCs provides an important avenue for design of miniature filters and power converters.
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    Design, Theoretical, and Experimental Investigation of Tensile-Strained Germanium Quantum-Well Laser Structure
    Hudait, Mantu K.; Murphy-Armando, Felipe; Saladukha, Dzianis; Clavel, Michael B.; Goley, Patrick S.; Maurya, Deepam; Bhattacharya, Shuvodip; Ochalski, Tomasz J. (American Chemical Society, 2021-10-14)
    Strain and band gap engineered epitaxial germanium (ϵ-Ge) quantum-well (QW) laser structures were investigated on GaAs substrates theoretically and experimentally for the first time. In this design, we exploit the ability of an InGaAs layer to simultaneously provide tensile strain in Ge (0.7-1.96%) and sufficient optical and carrier confinement. The direct band-to-band gain, threshold current density (Jth), and loss mechanisms that dominate in the ϵ-Ge QW laser structure were calculated using first-principles-based 30-band k·p electronic structure theory, at injected carrier concentrations from 3 × 1018 to 9 × 1019 cm-3. The higher strain in the ϵ-Ge QW increases the gain at higher wavelengths; however, a decreasing thickness is required by higher strain due to critical layer thickness for avoiding strain relaxation. In addition, we predict that a Jth of 300 A/cm2 can be reduced to <10 A/cm2 by increasing strain from 0.2% to 1.96% in ϵ-Ge lasing media. The measured room-temperature photoluminescence spectroscopy demonstrated direct band gap optical emission, from the conduction band at the Γ-valley to heavy-hole (0.6609 eV) from 1.6% tensile-strained Ge/In0.24Ga0.76As heterostructure grown by molecular beam epitaxy, is in agreement with the value calculated using 30-band k·p theory. The detailed plan-view transmission electron microscopic (TEM) analysis of 0.7% and 1.2% tensile-strained ϵ-Ge/InGaAs structures exhibited well-controlled dislocations within each ϵ-Ge layer. The measured dislocation density is below 4 × 106 cm-2 for the 1.2% ϵ-Ge layer, which is an upper bound, suggesting the superior ϵ-Ge material quality. Structural analysis of the experimentally realistic 1.95% biaxially strained In0.28Ga0.72As/13 nm ϵ-Ge/In0.28Ga0.72As QW structure demonstrated a strained Ge/In0.28Ga0.72As heterointerface with minimal relaxation using X-ray and cross-sectional TEM analysis. Therefore, our monolithic integration of a strained Ge QW laser structure on GaAs and ultimately the transfer of the process to the Si substrate via an InGa(Al)As/III-V buffer architecture would provide a significant step toward photonic technology based on strained Ge on a Si platform.
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    Dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites of BaTiO3 and 0.975BaTiO(3) 0.025Ba(Cu1/3Nb2/3)O-3
    Maurya, Deepam; Wongdamnern, Natthapong; Yimnirun, Rattikorn; Priya, Shashank (American Institute of Physics, 2010-12-15)
    In this paper, we report the dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites consisting of BaTiO3 (BT) and 0.975BaTiO(3)-0.025Ba(Cu1/3Nb2/3)O-3 (BTBCN). Two types of graded bilayer samples were synthesized, one with same thickness of BT and BTBCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BTBCN layers of equal thickness. Scanning electron microscopy and transmission electron microscopy images showed a sharp interface with needle-shape domains across the interface. The domain size on BT side was found to be larger than that on BTBCN side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting in characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BTBCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from polarization-electric field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area < A >, P-r, and E-C decreased with increasing frequency due to delayed response but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3514125]
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    Energy band alignment of atomic layer deposited HfO2 on epitaxial (110)Ge grown by molecular beam epitaxy
    Hudait, Mantu K.; Zhu, Y.; Maurya, Deepam; Priya, Shashank (AIP Publishing, 2013-03-01)
    The band alignment properties of atomic layer HfO2 film deposited on epitaxial (110)Ge, grown by molecular beam epitaxy, was investigated using x-ray photoelectron spectroscopy. The cross-sectional transmission electron microscopy exhibited a sharp interface between the (110)Ge epilayer and the HfO2 film. The measured valence band offset value of HfO2 relative to (110)Ge was 2.28 +/- 0.05 eV. The extracted conduction band offset value was 2.66 +/- 0.1 eV using the bandgaps of HfO2 of 5.61 eV and Ge bandgap of 0.67 eV. These band offset parameters and the interface chemical properties of HfO2/(110)Ge system are of tremendous importance for the design of future high hole mobility and low-power Ge-based metal-oxide transistor devices. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794838]
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    Enhanced piezoelectricity and nature of electric-field induced structural phase transformation in textured lead-free piezoelectric Na0.5Bi0.5TiO3-BaTiO3 ceramics
    Maurya, Deepam; Pramanick, Abhijit; An, Ke; Priya, Shashank (AIP Publishing, 2012-04-01)
    This letter provides a comparative description of the properties of textured and randomly oriented poly-crystalline lead-free piezoelectric 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO(3) (NBT-BT) ceramics. A high longitudinal piezoelectric constant of (d(33)) similar to 322 pC/N was obtained in (001)(PC) textured NBT-7BT ceramics, which is almost similar to 2x times the d(33) coefficient reported for randomly oriented ceramics of the same composition. In situ neutron diffraction experiments revealed that characteristically different structural responses are induced in textured and randomly oriented NBT-BT ceramics upon application of electric fields (E), which are likely related to the varying coherence lengths of polar nanoregions and internal stresses induced by domain switching. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709404]
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    Enhanced torsional actuation and stress coupling in Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO(3) lead-free piezoceramic system
    Berik, Pelin; Maurya, Deepam; Kumar, Prashant; Kang, Min-Gyu; Priya, Shashank (Taylor & Francis, 2017-01-01)
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    A generalized rule for large piezoelectric response in perovskite oxide ceramics and its application for design of lead-free compositions
    Ahn, Cheol-Woo; Maurya, Deepam; Park, Chee-Sung; Nahm, Sahn; Priya, Shashank (American Institute of Physics, 2009-06-01)
    We present a general rule for the perovskite oxide ceramics: "A large piezoelectric constant in ABO(3) perovskite ceramics can be obtained by tuning the weight ratio of A and B sites, WA/WB or WB/WA, to 3. Piezoelectric constant decreases significantly when WA/WB or WB/WA is in the range of 0.5-2.0, termed as forbidden zone." A comparative analysis was conducted for broad range of materials demonstrating the applicability of proposed rule. Further based on this rule optimized compositions in BaTiO3 and alkali niobate based systems were developed. Polycrystalline ceramics in modified BaTiO3 system were found to exhibit longitudinal piezoelectric coefficient (d(33)) of 330 pC/N, while alkali niobate ceramics showed d(33) of 294 pC/N. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3142442]
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    Giant energy density in 001 -textured Pb(Mg1/3Nb2/3)O-3-PbZrO3-PbTiO3 piezoelectric ceramics
    Yan, Yongke; Cho, Kyung-Hoon; Maurya, Deepam; Kumar, Amit; Kalinin, Sergei; Khachaturyan, Armen G.; Priya, Shashank (AIP Publishing, 2013-01-01)
    Pb(Zr,Ti)O-3 (PZT) based compositions have been challenging to texture or grow in a single crystal form due to the incongruent melting point of ZrO2. Here we demonstrate the method for achieving 90% textured PZT-based ceramics and further show that it can provide highest known energy density in piezoelectric materials through enhancement of piezoelectric charge and voltage coefficients (d and g). Our method provides more than similar to 5x increase in the ratio d(textured)/d(random). A giant magnitude of d.g coefficient with value of 59 000 x 10(-15) m(2) N-1 (comparable to that of the single crystal counterpart and 359% higher than that of the best commercial compositions) was obtained. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789854]
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    Giant piezoelectric voltage coefficient in grain-oriented modified PbTiO3 material
    Yan, Yongke; Zhou, Jie E.; Maurya, Deepam; Wang, Yu U.; Priya, Shashank (Springer Nature, 2016-10-11)
    A rapid surge in the research on piezoelectric sensors is occurring with the arrival of the Internet of Things. Single-phase oxide piezoelectric materials with giant piezoelectric voltage coefficient (g, induced voltage under applied stress) and high Curie temperature (T-c) are crucial towards providing desired performance for sensing, especially under harsh environmental conditions. Here, we report a grain-oriented (with 95% <001> texture) modified PbTiO3 ceramic that has a high T-c (364 degrees C) and an extremely large g(33) (115 x 10(-3) Vm N-1) in comparison with other known single-phase oxide materials. Our results reveal that self-polarization due to grain orientation along the spontaneous polarization direction plays an important role in achieving large piezoelectric response in a domain motion-confined material. The phase field simulations confirm that the large piezoelectric voltage coefficient g(33) originates from maximized piezoelectric strain coefficient d(33) and minimized dielectric permittivity epsilon(33) in [001]-textured PbTiO3 ceramics where domain wall motions are absent.
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    Giant strain with ultra-low hysteresis and high temperature stability in grain oriented lead-free K0.5Bi0.5TiO3-BaTiO3-Na0.5Bi0.5TiO3 piezoelectric materials
    Maurya, Deepam; Zhou, Yuan; Wang, Yaojin; Yan, Yongke; Li, Jiefang; Viehland, Dwight D.; Priya, Shashank (Springer Nature, 2015-02-26)
    We synthesized grain-oriented lead-free piezoelectric materials in (K0.5Bi0.5TiO3-BaTiO3-xNa(0.5)Bi(0.5)TiO(3) (KBT-BT-NBT) system with high degree of texturing along the [001]c (c-cubic) crystallographic orientation. We demonstrate giant field induced strain (similar to 0.48%) with an ultra-low hysteresis along with enhanced piezoelectric response (d(33) similar to 190pC/N) and high temperature stability (similar to 160 degrees C). Transmission electron microscopy (TEM) and piezoresponse force microscopy (PFM) results demonstrate smaller size highly ordered domain structure in grain-oriented specimen relative to the conventional polycrystalline ceramics. The grain oriented specimens exhibited a high degree of non-180 degrees domain switching, in comparison to the randomly axed ones. These results indicate the effective solution to the lead-free piezoelectric materials.
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    Integration of lead-free ferroelectric on HfO2/Si (100) for high performance non-volatile memory applications
    Kundu, Souvik; Maurya, Deepam; Clavel, Michael B.; Zhou, Yuan; Halder, Nripendra N.; Hudait, Mantu K.; Banerji, Pallab; Priya, Shashank (Nature Publishing Group, 2015-02-16)
    We introduce a novel lead-free ferroelectric thin film (1-x)BaTiO3-xBa(Cu1/3Nb2/3)O3 (x 5 0.025) (BT-BCN) integrated on to HfO2 buffered Si for non-volatile memory (NVM) applications. Piezoelectric force microscopy (PFM), x-ray diffraction, and high resolution transmission electron microscopy were employed to establish the ferroelectricity in BT-BCN thin films. PFMstudy reveals that the domains reversal occurs with 1806 phase change by applying external voltage, demonstrating its effectiveness forNVMdevice applications. X-ray photoelectron microscopy was used to investigate the band alignments between atomic layer deposited HfO2 and pulsed laser deposited BT-BCN films. Programming and erasing operations were explained on the basis of band-alignments. The structure offers large memory window, low leakage current, and high and low capacitance values that were easily distinguishable even after ,106 s, indicating strong charge storage potential. This study explains a new approach towards the realization of ferroelectric based memory devices integrated on Si platform and also opens up a new possibility to embed the system within current complementary metal-oxide-semiconductor processing technology.
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    Interfacial band alignment and structural properties of nanoscale TiO2 thin films for integration with epitaxial crystallographic oriented germanium
    Jain, Nikhil; Zhu, Yizheng; Maurya, Deepam; Varghese, Ronnie; Priya, Shashank; Hudait, Mantu K. (American Institute of Physics, 2014-01-14)
    We have investigated the structural and band alignment properties of nanoscale titanium dioxide (TiO2) thin films deposited on epitaxial crystallographic oriented Ge layers grown on (100), (110), and (111) A GaAs substrates by molecular beam epitaxy. The TiO2 thin films deposited at low temperature by physical vapor deposition were found to be amorphous in nature, and high-resolution transmission electron microscopy confirmed a sharp heterointerface between the TiO2 thin film and the epitaxially grown Ge with no traceable interfacial layer. A comprehensive assessment on the effect of substrate orientation on the band alignment at the TiO2/Ge heterointerface is presented by utilizing x-ray photoelectron spectroscopy and spectroscopic ellipsometry. A band-gap of 3.33 +/- 0.02 eV was determined for the amorphous TiO2 thin film from the Tauc plot. Irrespective of the crystallographic orientation of the epitaxial Ge layer, a sufficient valence band-offset of greater than 2 eV was obtained at the TiO2/Ge heterointerface while the corresponding conduction band-offsets for the aforementioned TiO2/Ge system were found to be smaller than 1 eV. A comparative assessment on the effect of Ge substrate orientation revealed a valence band-offset relation of Delta E-V(100)> Delta E-V(111)> Delta E-V(110) and a conduction band-offset relation of Delta E-C(110) > Delta E-C(111)> Delta E-C(100). These band-offset parameters are of critical importance and will provide key insight for the design and performance analysis of TiO2 for potential high-k dielectric integration and for future metal-insulator-semiconductor contact applications with next generation of Ge based metal-oxide field-effect transistors. (C) 2014 AIP Publishing LLC.
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    Magnetoelectric Interactions in Lead-Based and Lead-Free Composites
    Bichurin, Mirza I.; Petrov, Vladimir M.; Zakharov, Anatoly; Kovalenko, Denis; Yang, Su-Chul; Maurya, Deepam; Bedekar, Vishwas; Priya, Shashank (MDPI, 2011-04-06)
    Magnetoelectric (ME) composites that simultaneously exhibit ferroelectricity and ferromagnetism have recently gained significant attention as evident by the increasing number of publications. These research activities are direct results of the fact that multiferroic magnetoelectrics offer significant technological promise for multiple devices. Appropriate choice of phases with co-firing capability, magnetostriction and piezoelectric coefficient, such as Ni-PZT and NZFO-PZT, has resulted in fabrication of prototype components that promise transition. In this manuscript, we report the properties of Ni-PZT and NZFO-PZT composites in terms of ME voltage coefficients as a function of frequency and magnetic DC bias. In order to overcome the problem of toxicity of lead, we have conducted experiments with Pb-free piezoelectric compositions. Results are presented on the magnetoelectric performance of Ni-NKN, Ni-NBTBT and NZFO-NKN, NZFO-NBTBT systems illustrating their importance as an environmentally friendly alternative.
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    A new method for achieving enhanced dielectric response over a wide temperature range
    Maurya, Deepam; Sun, Fu-Chang; Alpay, S. Pamir; Priya, Shashank (Springer Nature, 2015-10-19)
    We report a novel approach for achieving high dielectric response over a wide temperature range. In this approach, multilayer ceramic heterostructures with constituent compositions having strategically tuned Curie points (T-C) were designed and integrated with varying electrical connectivity. Interestingly, these multilayer structures exhibited different dielectric behavior in series and parallel configuration due to variations in electrical boundary conditions resulting in the differences in the strength of the electrostatic coupling. The results are explained using nonlinear thermodynamic model taking into account electrostatic interlayer interaction. We believe that present work will have huge significance in design of high performance ceramic capacitors.
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    Origin of high piezoelectric response in A-site disordered morphotropic phase boundary composition of lead-free piezoelectric 0.93(Na0.5Bi0.5)TiO3-0.07BaTiO(3)
    Maurya, Deepam; Murayama, Mitsuhiro; Pramanick, A.; Reynolds, William T. Jr.; An, Ke; Priya, Shashank (American Institute of Physics, 2013-03-21)
    Perovskite piezoelectric compositions near the morphotropic phase boundary (MPB) are known to exhibit high piezoelectric response. In lead-based ABO(3) compound with B-site disorder, the origin of this enhancement has been associated with the presence of an intermediate monoclinic/orthorhombic state that bridges the adjacent ferroelectric rhombohedral and tetragonal phases. However, the origin of high piezoelectric response in lead-free ABO(3) compounds with A-site disorder has not been conclusively established. We describe a microscopic model derived from comparative analyses of high resolution transmission electron microscopy and neutron diffraction that explains the origin of high piezoelectric response in lead-free MPB compositions of 0.93(Na0.5Bi0.5)TiO3-0.07BaTiO3. Direct observation of nanotwins with monoclinic symmetry confirmed the presence of an intermediate bridging phase that facilitates a pathway for polarization reorientation. Monoclinic distortions of an average rhombohedral phase are attributed to localized displacements of atoms along the non-polar directions. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792729]
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    Processing method for grain-oriented lead-free piezoelectric Na0.5Bi0.5TiO3—BaTiO3 ceramics exhibiting giant performance
    (United States Patent and Trademark Office, 2017-09-26)
    Textured ceramic compositions having improved piezoelectric characteristics as compared with their random counterparts are provided. Methods of making the compositions and devices using them are also included. More particularly, compositions comprising textured ceramic Na0.5Bi0.5TiO3—BaTiO3(NBT-BT) materials synthesized from high aspect ratio NBT seeds exhibit improved characteristics, including an increased longitudinal piezoelectric constant (d33) and magnetoelectric coupling coefficient over randomly oriented NBT-BT. Additionally provided are compositions comprising of nanostructured Na0.5Bi0.5TiO3—BaTiO3 ferroelectric whiskers having a high aspect ratio. Nanostructured whiskers can be used to improve the piezoelectric properties of the bulk ceramics. The inventive materials are useful in microelectronic devices, with some finding particular application as multilayer actuators and transducers.
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    Processing, Structure and Properties of High Temperature Thermoelectric Oxide Materials
    Song, Myung-Eun (Virginia Tech, 2018-11-30)
    High temperature thermal energy harvesting has attracted much attention recently. In order to achieve stable operation at high temperatures there is emerging need to develop efficient and oxidation-resistant materials. Most of the well-known materials with high dimensionless figure of merit (ZT) values such as Bi2Te3, PbTe, skutterudites, and half-Heusler alloys, are not thermally stable at temperatures approaching 500°C or higher, due to the presence of volatile elements. Oxide thermoelectric materials are considered to be potential candidates for high temperature applications due to their robust thermal and chemical stability in oxidizing atmosphere along with the reduced toxicity, relatively simpler fabrication, and cost. In this dissertation, nanoscale texturing and interface engineering were utilized for enhancing the thermoelectric performance of oxide polycrystalline Ca3Co4O9 materials, which were synthesized using conventional sintering and spark plasma sintering (SPS) techniques. In order to tailor the electrical and thermal properties, Lu and Ga co-doping was investigated in Ca3Co4O9 system. The effect of co-doping at Ca and Co sites on the thermoelectric properties was quantified and the anisotropic behavior was investigated. Because of the effective scattering of phonons by doping-induced defects, lower thermal conductivity and higher ZT were achieved. The layered structure of Ca3Co4O9 has strong anisotropy in the transport properties. For this reason, the thermoelectric measurements were conducted for the samples along both vertical and horizontal directions. The ZT value along the vertical direction was found to be 3 to 4 times higher than that along the horizontal direction. Metallic inclusions along with ionic doping were also utilized in order to enhance the ZT of Ca3Co4O9. The texturing occurring in the nanostructured Ca3Co4O9 through ion doping and Ag inclusions was studied using microscopy and diffraction analysis. Multi-length scale inclusions and heavier ion doping in Ca3Co4O9 resulted in higher electrical conductivity and reduced thermal conductivity. The maximum ZT of 0.25 at 670°C was found in the spark plasma sintered Ca2.95Ag0.05Co4O9 sample. In literature, limited number of studies have been conducted on understanding the anisotropic thermoelectric performance of Ca3Co4O9, which often results in erroneous estimation of ZT. This study addresses this limitation and provides systematic evaluation of the anisotropic response with respect to platelet microstructure. Textured Ca3Co4O9/Ag nanocomposites were fabricated using spark plasma sintering (SPS) technique and utilized for understanding the role of microstructure towards anisotropic thermoelectric properties. The thermoelectric response was measured along both vertical and horizontal direction with respect to the SPS pressure axis. In order to achieve enhanced degree of texturing and increase electrical conductivity along ab planes, a two-step SPS method was developed. Ag nanoinclusions was found to increase the overall electrical conductivity and the thermoelectric power factor because of improved electrical connections among the grains. Through two-step SPS method, 28% improvement in the average ZT values below 400°C and 10% improvement above 400°C in Ca3Co4O9/Ag nanocomposites was achieved. Lastly, this dissertation provides significant progress towards understanding the effect of synthesis method on thermoelectric properties and evolution of textured microstructure. The anisotropy resulting from the crystal structure and microstructural features is systematically quantified. Results reported in this study will assist the continued progress in developing Ca3Co4O9 materials for practical thermoelectric applications.
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    Quasi-zero lattice mismatch and band alignment of BaTiO3 on epitaxial (110)Ge
    Hudait, Mantu K.; Zhu, Yizheng; Jain, Nikhil; Maurya, Deepam; Zhou, Y.; Priya, Shashank (American Institute of Physics, 2013-07-14)
    Growth, structural, and band alignment properties of pulsed laser deposited amorphous BaTiO3 on epitaxial molecular beam epitaxy grown (110) Ge layer, as well as their utilization in low power transistor are reported. High-resolution x-ray diffraction demonstrated quasi-zero lattice mismatch of BaTiO3 on (110) Ge. Cross-sectional transmission electron microscopy micrograph confirms the amorphous nature of BaTiO3 layer as well as shows a sharp heterointerface between BaTiO3 and Ge with no traceable interfacial layer. The valence band offset, Delta E-v, of 1.99 +/- 0.05 eV at the BaTiO3/(110) Ge heterointerface is measured using x-ray photoelectron spectroscopy. The conduction band offset, Delta E-c, of 1.14 +/- 0.1 eV is calculated using the bandgap energies of BaTiO3 of 3.8 eV and Ge of 0.67 eV. These band offset parameters for carrier confinement and the interface chemical properties of the BaTiO3/(110) Ge system are significant advancement towards designing Ge-based p-and n-channel metal-oxide semiconductor field-effect transistors for low-power application. (C) 2013 AIP Publishing LLC.