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Nanopatterned ferroelectrics for ultrahigh density rad-hard nonvolatile memories.

Description: Radiation hard nonvolatile random access memory (NVRAM) is a crucial component for DOE and DOD surveillance and defense applications. NVRAMs based upon ferroelectric materials (also known as FERAMs) are proven to work in radiation-rich environments and inherently require less power than many other NVRAM technologies. However, fabrication and integration challenges have led to state-of-the-art FERAMs still being fabricated using a 130nm process while competing phase-change memory (PRAM) has been demonstrated with a 20nm process. Use of block copolymer lithography is a promising approach to patterning at the sub-32nm scale, but is currently limited to self-assembly directly on Si or SiO{sub 2} layers. Successful integration of ferroelectrics with discrete and addressable features of {approx}15-20nm would represent a 100-fold improvement in areal memory density and would enable more highly integrated electronic devices required for systems advances. Towards this end, we have developed a technique that allows us to carry out block copolymer self-assembly directly on a huge variety of different materials and have investigated the fabrication, integration, and characterization of electroceramic materials - primarily focused on solution-derived ferroelectrics - with discrete features of {approx}20nm and below. Significant challenges remain before such techniques will be capable of fabricating fully integrated NVRAM devices, but the tools developed for this effort are already finding broader use. This report introduces the nanopatterned NVRAM device concept as a mechanism for motivating the subsequent studies, but the bulk of the document will focus on the platform and technology development.
Date: September 1, 2010
Creator: Brennecka, Geoffrey L.; Stevens, Jeffrey; Scrymgeour, David; Gin, Aaron V. & Tuttle, Bruce Andrew
Partner: UNT Libraries Government Documents Department

Equivalence of dipole correction and Coulomb cutoff techniques in supercell calculations

Description: Article on the equivalence of dipole correction and Coulomb cutoff techniques in supercell calculations. In this work, the authors compare the dipole correction and Coulomb cutoff methods under the same conditions in the framework of plane-wave based density-functional theory.
Date: June 3, 2008
Creator: Yu, Liping; Ranjan, Vivek; Lu, W.; Bernholc, Jerry & Buongiorno Nardelli, Marco
Partner: UNT College of Arts and Sciences

On the long-time behavior of ferroelectric systems

Description: In this note we investigate a new model for the behavior of ferroelectric materials. This model is analogous to one used in [1] to describe the dynamics of elastic materials which exhibit phase changes.
Date: July 16, 2003
Creator: Greenberg, J. M.; MacCamy, R. C. & Coffman, C. V.
Partner: UNT Libraries Government Documents Department

Phase transformation of PZST-86/14-5-2Nb ceramic under quasi-static loading conditions.

Description: Specimens of poled and unpoled PZST ceramic were tested under hydrostatic loading conditions at temperatures of -55, 25, and 75 C. The objective of this experimental study was to obtain the electro-mechanical properties of the ceramic and the criteria of FE (Ferroelectric) to AFE (Antiferroelectric) phase transformations of the PZST ceramic to aid grain-scale modeling efforts in developing and testing realistic response models for use in simulation codes. As seen in previous studies, the poled ceramic from PZST undergoes anisotropic deformation during the transition from a FE to an AFE phase at -55 C. Warmer temperature tests exhibit anisotropic deformation in both the FE and AFE phase. The phase transformation is permanent at -55 C for all ceramics tests, whereas the transformation can be completely reversed at 25 and 75 C. The change in the phase transformation pressures at different temperatures were practically identical for both unpoled and poled PZST specimens. Bulk modulus for both poled and unpoled material was lowest in the FE phase, intermediate in the transition phase, and highest in the AFE phase. Additionally, bulk modulus varies with temperature in that PZST is stiffer as temperature decreases. Results from one poled-biased test for PZST and four poled-biased tests from PNZT 95/5-2Nb are presented. A bias of 1kV did not show noticeable differences in phase transformation pressure for the PZST material. However, with PNZT 95/5-2Nb phase transformation pressure increased with increasing voltage bias up to 4.5kV.
Date: February 1, 2010
Creator: Broome, Scott Thomas; Scofield, Timothy W.; Montgomery, Stephen Tedford; Bauer, Stephen J. & Hofer, John H.
Partner: UNT Libraries Government Documents Department

Nanoscale Structural Engineering of Ferroelectric Polymers. Final Report for July 2001-June 2005

Description: This final report describes the interaction between multilavered films of polymer ferroelectrics, in our case the copolymers of PVDF formed with TrFE. Langmuir Blodgett deposition of these films allows the deposition of thin, uniform, highly crystalline films. Two type of multilayer stacks are made and characterized. The first consists of multilayer stacks of the copolymer films with 2 different TrFE contents-50% and 20%. By varying the period of the multilayer stacks we see evidence of interaction at short length scales, evidenced in the thermodynamic transition temperatures of the multilayer films. The second set consists of a P(VDF - TrFE) film sandwiched between two Cobalt electrodes. In these we see evidence of a large magnetoelectric coupling.
Date: December 1, 2005
Creator: Adenwalla, S.
Partner: UNT Libraries Government Documents Department


Description: Progress is briefly reported on studies in dielectric spectros copy, magnetic resonance, high-field-strength research, ferroelectrics and ferromagnetics, semiconductors, single crystals, and ceramics. (T.R.R.)
Date: June 1, 1958
Partner: UNT Libraries Government Documents Department

Non-traditional solution routes to ferroelectric materials

Description: Non-traditional precursor solutions for production of ferroelectric thin films have been developed for PXZT (X = L, N, S), SBT, and PMN systems. For PXZT and SBT, pyridine is a key solvent, wherein, it both solubilizes and reduces the reactivity of the individual components of the solution. Further control of the final films has been obtained using novel tailor-made precursors to dictate their properties.
Date: April 1, 1997
Creator: Boyle, T.J.; Buchheit, C.D. & Al-Shareef, H.N.
Partner: UNT Libraries Government Documents Department

Tuning ground states and excitations in complex electronic materials

Description: Modern electronic materials are characterized by a great variety of broken-symmetry ground states and excitations. Their control requires understanding and tuning underlying driving forces of spin-charge-lattice coupling, critical to macroscopic properties and applications. We report representative model calculations which demonstrate some of the richness of the phenomena and the challenges for successful microscopic modeling.
Date: September 1, 1996
Creator: Bishop, A.R.
Partner: UNT Libraries Government Documents Department

Pressure as a probe of the physics of ABO{sub 3} relaxor ferroelectrics

Description: Results on a variety of mixed ABO{sub 3} oxides have revealed a pressure-induced ferroelectric-to-relaxor crossover and the continuous evolution of the energetics and dynamics of the relaxation process with increasing pressure. These common features have suggested a mechanism for the crossover phenomenon in terms of a large decrease in the correlation length for dipolar interactions with pressure--a unique property of soft mode or highly polarizable host lattices. The pressure effects as well as the interplay between pressure and dc biasing fields are illustrated for some recent results on PZN-9.5 PT,PMN and PLZT 6/65/35.
Date: February 14, 2000
Partner: UNT Libraries Government Documents Department

Study of the structure of ferroelectric domain walls in barium titanate ceramics

Description: Structure of 90{degree} ferroelectric domain boundaries in barium titanate ceramics has been studied by means of Transmission Electron Microscopy and High Resolution TEM. Tilts of specific fringes across domain walls are measured on HREM images and Selected Area Diffraction Patterns. They are in a good agreement with the twin model admitted for these domain boundaries. A computerized method has been developed to give access to quantitative information about atomic displacements across these ferroelectric domain walls. The so calculated displacement field is then compared with Landau-Ginzburg based theoretical predictions.
Date: February 1, 1995
Creator: Normand, L.; Thorel, A.; Kilaas, R. & Montardi, Y.
Partner: UNT Libraries Government Documents Department

Solution Synthesis and Processing of PZT Materials for Neutron Generator Applications

Description: A new solution synthesis route has been developed for the preparation of lead-based ferroelectric materials (patent filed). The process produces controlled stoichiometry precursor powders by non-aqueous precipitation. For a given ferroelectric material to be prepared, a metal acetate/alkoxide solution containing constituent metal species in the appropriate ratio is mixed with an oxalic acid/n-propanol precipitant solution. An oxalate coprecipitate is instantly fonned upon mixing that quantitatively removes the metals from solution. Most of the process development was focused on the synthesis and processing of niobium-substituted lead zirconate titanate with a Zr-to-Ti ratio of 95:5 (PNZT 95/5) that has an application in neutron generator power supplies. The process was scaled to produce 1.6 kg of the PNZT 95/5 powder using either a sen-ii-batch or a continuous precipitation scheme. Several of the PNZT 95/5 powder lots were processed into ceramic slug form. The slugs in turn were processed into components and characterized. The physical properties and electrical performance (including explosive functional testing of the components met the requirements set for the neutron generator application. Also, it has been demonstrated that the process is highly reproducible with respect to the properties of the powders it produces and the properties of the ceramics prepared from its powders. The work described in this report was funded by Sandia's Laboratory Directed Research and Development Program.
Date: December 1, 1998
Creator: Anderson, M.A.; Ewsuk, K.G.; Montoya, T.V.; Moore, R.H.; Sipola, D.L.; Tuttle, B.A. et al.
Partner: UNT Libraries Government Documents Department

Optical properties of epitaxial PLT thin films

Description: Metalorganic chemical vapor deposition was used to prepare epitaxial or highly oriented PLT (Pb{sub 1-x}La{sub x}TiO{sub 3}) thin films with x = 0.21-0.34. The growth of PLT films resulted in 3-D epitaxial heterostructures on a (100) surface of both MgO and KTaO{sub 3} substrates. The PLT film grown on a KTaO{sub 3} (100) substrate has a significantly lower minimum channeling yield compared to that grown on the MgO (100) substrate because of the smaller lattice mismatch associated with KTaO{sub 3}. Thickness and refractive indices at 435-1523 nm were measured by prism coupling. Measured film thickness of 570 nm was in good agreement with that obtained from RBS. Refractive index of the PLT film is smaller than that of PbTiO{sub 3}, and its difference at {lambda} = 632.8 nm is about 2.5%. Dispersion of the refractive index was well fitted by a Sellmeier dispersion formula.
Date: January 1, 1996
Creator: Kim, Y.; Erbil, A.; Boatner, L.A.; Steingart, L.; Mensah, T. & Hiamang, S.
Partner: UNT Libraries Government Documents Department

Measurement and calculation of PZT thin film longitudinal piezoelectric coefficients.

Description: The ferroelectric and piezoelectric properties of 2000 {angstrom} thick chemical solution deposited Pb(Zr{sub x}Ti{sub 1{minus}x})O{sub 3} (PZT) thin films were investigated. Several Zr/Ti ratios were studied: 30/70, 50/50 and 65/35, which correspond to tetragonal, near-morphotropic, and rhombohedral symmetries. In all samples, a {l_brace}111{r_brace}-texture is predominant. Longitudinal piezoelectric coefficients and their dc field dependence were measured using the contact AFM method. The expected trend of a maximum piezoelectric coefficient at or near to the MPB was not observed. The composition dependence was small, with the maximum d{sub 33} occurring in the tetragonal material. To explain the results, crystallographic texture and film thickness effects are suggested. Using a modified phenomenological approach, derived electrostrictive coefficients, and experimental data, d{sub 33} values were calculated. Qualitative agreement was observed between the measured and calculated coefficients. Justifications of modifications to the calculations are discussed.
Date: April 26, 1999
Creator: Christman, J. A.; Kim, S.-H.; Kingon, A. I.; Maiwa, H.; Maria, J.-P. & Streiffer, S. K.
Partner: UNT Libraries Government Documents Department

Uniaxial Compression Experiments on Lead Zirconate Titanate 95/5-2Nb Ceramic: Evidence for an Orientation-Dependent, ''Maximum Compressive Stress'' Criterion for Onset of the Ferroelectric - Antiferroelectric Polymorphic Transformation

Description: Some time ago we presented evidence that, under nonhydrostatic loading, the F{sub R1} {r_arrow} A{sub O} polymorphic transformation of unpoled PZT 95/5-2Nb (PNZT) ceramic began when the maximum compressive stress equaled the hydro-static pressure at which the transformation otherwise took place. Recently we showed that this simple criterion did not apply to nonhydrostatically compressed, poled ceramic. However, unpoled ceramic is isotropic, whereas poled ceramic has a preferred crystallographic orientation and is mechanically anisotropic. If we further assume that the transformation depends not only on the magnitude of the compressive stress, but also its orientation relative to some feature(s) of PNZT's crystallography, then these disparate results can be qualitatively resolved. It has long been known that this transformation can be triggered in uniaxial compression. Our modified hypothesis makes two predictions for transformation of unpoled polycrystals under uniaxial stress: (i) the transformation should begin when the maximum compressive stress, {sigma}{sub 1}, equals the hydrostatic pressure for transformation, and (ii) a steadily increasing axial stress should be required to drive the transformation.
Date: July 26, 1999
Creator: Zeuch, D. H.; Montgomery, S. T. & Holcomb, D. J.
Partner: UNT Libraries Government Documents Department

Chem-Prep PZT 95/5 for Neutron Generator Applications: Particle Size Distribution Comparison of Development and Production-Scale Powders

Description: The Materials Chemistry Department 1846 has developed a lab-scale chem-prep process for the synthesis of PNZT 95/5, a ferroelectric material that is used in neutron generator power supplies. This process (Sandia Process, or SP) has been successfully transferred to and scaled by Department 14192 (Ceramics and Glass Department), (Transferred Sandia Process, or TSP), to meet the future supply needs of Sandia for its neutron generator production responsibilities. In going from the development-size SP batch (1.6 kg/batch) to the production-scale TSP powder batch size (10 kg/batch), it was important that it be determined if the scaling process caused any ''performance-critical'' changes in the PNZT 95/5 being produced. One area where a difference was found was in the particle size distributions of the calcined PNZT powders. Documented in this SAND report are the results of an experimental study to determine the origin of the differences in the particle size distribution of the SP and TSP powders.
Date: July 1, 2002
Partner: UNT Libraries Government Documents Department

Nanoscale investigation of polarization retention loss in ferroelectric thin films via scanning force microscopy.

Description: Scanning force microscopy (SFM) was applied to direct nanoscale investigation of the mechanism of retention loss in ferroelectric thin films. Experiments were conducted by performing local polarization reversal within an individual grain with subsequent imaging of a resulting domain structure at various time intervals. A conductive SFM tip was used for domain switching and imaging in the SFM piezoresponse mode.
Date: February 12, 1998
Creator: Aggarwal, S.; Auciello, O.; Gruverman, A.; Prakash, S. A.; Ramesh, R. & Tokumoto, H.
Partner: UNT Libraries Government Documents Department

Emission from ferroelectric cathodes

Description: We have recently initiated an investigation of electron emission from ferroelectric cathodes. Our experimental apparatus consisted of an electron diode and a 250 kV, 12 ohm, 70 ns pulsed high voltage power source. A planar triode modulator driven by a synthesized waveform generator initiates the polarization inversion and allows inversion pulse tailoring. The pulsed high voltage power source is capable of delivering two high voltage pulses within 50 ns of each other and is capable of operating at a sustained repetition rate of 5 Hz. Our initial measurements indicate that emission current densities above the Child-Langmuir Space Charge Limit are possible. We explain this effect to be based on a non-zero initial energy of the emitted electrons. We also determined that this effect is strongly coupled to relative timing between the inversion pulse and application of the main anode-cathode pulse. We also have initiated brightness measurements of the emitted beam. As in our previous measurements at this Laboratory, we performed the measurement using a pepper pot technique. Beam-let profiles are recorded with a fast phosphor and gated cameras. We describe our apparatus and preliminary measurements.
Date: May 17, 1993
Creator: Sampayan, S. E.; Caporaso, G. J.; Holmes, C. L.; Lauer, E. J.; Prosnitz, D.; Trimble, D. O. et al.
Partner: UNT Libraries Government Documents Department

Time-of-flight pulsed ion beam surface analysis as a means of in situ, real-time characterization of the growth of ferro-electric and conductive oxide heterostructures

Description: Pulsed beam Time-of-Flight Ion Scattering and Recoil Spectroscopy (TOF-ISARS) surface analysis methods have been developed which permit real-time, in situ characterization of the growth layer of multi-component oxide thin films. Results are presented from a study of the deposition of Pb, Zr, Ti and Ru using a sequential layer-by-layer deposition method under ambient oxygen pressure conditions appropriate to the growth of PZT films, revealing layer-by-layer as well as 2D and 3D island growth processes during deposition. Thermodynamic stability conditions result in modification of the layered structure, during deposition, in some cases altering the layer ordering of the growth region. Calculations using the Miedema model for surface segregation are in accord with experimental results that reveal an exchange between deposited Zr and Ti atoms and an underlying Pb layer. In addition, the room temperature studies revealed that Pb grows layer-by-layer, nucleating as 2D islands, while Zr tends to form three-dimensional islands. At room temperature, the Zr surface concentration is strongly enhanced by the presence of oxygen, but at high temperatures, surface Pb is found to be stabilized by the presence of an oxygen ambient, illustrating the importance of real-time, in situ analysis of the growth layer as opposed to more conventional surface analytical methods which require interruption of the deposition process in order to characterize the film surface.
Date: April 1, 1994
Creator: Krauss, A. R.; Gruen, D. M.; Auciello, O.; Lin, Y. & Chang, R. P. H.
Partner: UNT Libraries Government Documents Department

Remarkable Strontium B-Site Occupancy in FerroelectricPb(Zr1-xTix)O3 Solid Solutions Doped with Cryolite-Type StrontiumNiobate

Description: New high-performance ferroelectric materials based on Pb(Zr{sub 1-x}Ti{sub x})O{sub 3} (PZT) that are doped with cryolite-type strontium niobate (SNO, Sr{sub 4}(Sr{sub 2-2y/3}Nb{sub 2+2y/3})O{sub 11+y}V{sub 0,1-y} with 0 {le} y {le} 1), hence denoted PZT:SNO, and their microscopic structure are described. The combination of exceptional piezoelectric properties, i.e. a piezoelectric strain constant of d{sub 33} {approx} 760 pm/V, with excellent stability and degradation resistance makes ferroelectric PZT:SNO solid solutions very attractive for use in novel and innovative piezoelectric actuator and transducer applications. Extended X-ray absorption fine-structure (EXAFS) analyses of PZT:SNO samples revealed that {approx}10 % of the Sr cations occupy the nominal B-sites of the perovskite-type PZT host lattice. This result was supported by EXAFS analyses of both a canonical SrTiO{sub 3} perovskite and two SNO model and reference compounds. Fit models that do not account for Sr cations on B-sites were ruled out. A clear Sr-Pb peak in Fourier transformed EXAFS data visually confirmed this structural model. The generation of temporary oxygen vacancies and the intricate defect chemistry induced by SNO-doping of PZT are crucial for the exceptional materials properties exhibited by PZT:SNO materials.
Date: April 26, 2007
Creator: Feltz, A.; Schmidt-Winkel, P.; Schossman, M.; Booth, C.H. & Albering, J.
Partner: UNT Libraries Government Documents Department