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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Effect of (Sr{sub 0.7}Ca{sub 0.3})TiO{sub 3}-substitution on structure, dielectric, ferroelectric, and magnetic properties of BiFeO{sub 3} ceramics

Bi{sub 1−x}(Sr{sub 0.7}Ca{sub 0.3}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} ceramics were prepared by a standard solid state reaction process, and the influence of Sr/Ca ratio on structure and properties for Bi{sub 1−x}(Sr,Ca){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} system was discussed by comparing with Sr{sub 0.5}Ca{sub 0.5}TiO{sub 3}-modified BiFeO{sub 3} ceramics. Rietveld analysis of X-ray diffraction data revealed that the crystal structure changed from rhombohedral R3c (x ≤ 0.4) to orthorhombic Pnma (x = 0.6) with Sr{sub 0.7}Ca{sub 0.3}TiO{sub 3} substitution, and biphasic structure (R3c + Pnma) was determined at x = 0.5, while that for Bi{sub 1−x}(Sr{sub 0.5}Ca{sub 0.5}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} system was at x = 0.4. This indicated that the morphotropic phase boundary in Bi{sub 1−x}(Sr,Ca){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} system shifted toward (Sr,Ca)TiO{sub 3} side with increasing Sr/Ca ratio. The Raman spectrometric analysis and selected area electron diffraction analysis also confirmed this transition. The dielectric relaxation could be well fitted by Arrhenius law, and the different activation energies were attributed to the different origins of the dielectric relaxations with increasing temperature. The current density-field (J-E) curves indicated that the leakage current was reduced to about five orders of magnitude with Sr{sub 0.7}Ca{sub 0.3}TiO{sub 3} substitution. The P-E hysteresis loops obtained by three different methods indicated the enhanced ferroelectricity at x = 0.4, and it could be attributed to the decrement of leakage current. Meanwhile, the magnetization was enhanced with Sr{sub 0.7}Ca{sub 0.3}TiO{sub 3} substitution, and the maximum remanent magnetization was determined at x = 0.2. The enhanced magnetization originated from the partial substitution of Fe{sup 3+} by Ti{sup 4+}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Studies of electrical conductivity and complex initial permeability of multiferroic xBa{sub 0.95}Sr{sub 0.05}TiO{sub 3}-(1-x)BiFe{sub 0.90}Gd{sub 0.10}O{sub 3} ceramics

Multiferroic xBa{sub 0.95}Sr{sub 0.05}TiO{sub 3}-(1-x)BiFe{sub 0.90}Gd{sub 0.10}O{sub 3} [xBST-(1-x)BFGO] (x = 0.00, 0.10 and 0.20) ceramics were prepared by the standard solid-state reaction technique. Crystal structure of the ceramics was determined by X-ray diffraction pattern. All the compositions exhibited rhombohedral crystal structure. The tolerance factor ‘t’ varied from 0.847 to 0.864. The AC conductivity spectrum followed the Jonscher’s power law. The Nyquist plots indicated that only grains have the contribution to the resistance in this material and the values of grain resistance (R{sub g}) increased with BST content. The real part of complex initial permeability decreased with the increase in frequency and increased with increasing BST content. Magnetoelectric coefficient was determined for all compositions. The maximum value of magnetoelectric coefficient was found to be 1.467 mV.cm{sup −1}.Oe{sup −1} for x = 0.20.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Morphotropic NaNbO{sub 3}-BaTiO{sub 3}-CaZrO{sub 3} lead-free ceramics with temperature-insensitive piezoelectric properties

A morphotropic NaNbO{sub 3}-based lead-free ceramic was reported to have temperature-insensitive piezoelectric and electromechanical properties (d{sub 33} = 231 pC/N, k{sub p} = 35%, T{sub c} = 148 °C, and low-hysteresis strain ∼0.15%) in a relatively wide temperature range. This was fundamentally ascribed to the finding of a composition-axis vertical morphotropic phase boundary in which coexisting ferroelectric phases are only compositionally driven and thermally insensitive. Both phase coexistence and nano-scaled domain morphology deserved well enhanced electrical properties, as evidenced by means of synchrotron x-ray diffraction and transmission electron microscopy. Our study suggests that the current lead-free ceramic would be a very promising piezoelectric material for actuator and sensor applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructural analysis and thermoelectric properties of Sn-Al co-doped ZnO ceramics

Sn-Al co-doped polycrystalline ZnO ceramics were prepared by sintering in air. Phase and microstructure analysis was performed by X-ray diffraction and SEM-EDS and thermoelectric properties were measured. XRD analysis showed a ZnO primary phase as well as secondary phase peaks due to the formation of a Zn{sub 2}SnO{sub 4} spinel phase or SnO{sub 2}(ZnO:Sn-Al){sub m} intergrowth phase. SEM analysis revealed a dense microstructure with a small number of nanometric pores, consistent with the measured density of 5.48 g/cm{sup 3}. An activated electrical conductivity characteristic of a semiconducting material was observed as well as a negative Seebeck coefficient with both values increasing in absolute value from RT to 730 °C. The power factor had a maximum value of 3.73×10{sup −4} W m{sup −1} K{sup −2} at 730 °C. Thermal conductivity measurements showed a significant reduction over the measured temperature range compared to undoped ZnO. This could be attributed to grain size reduction, the formation of a nanoscale secondary phase or a reduction in crystallinity caused by Sn-Al co-doping. A maximum ZT of 0.06 was obtained at 750 °C for the Sn-Al co-doped ZnO ceramics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Compositionally complex carbide ceramics: A perspective on irradiation damage

Extensive experimental and computational studies have demonstrated outstanding physical and chemical properties of the novel materials of compositionally complex carbides (CCCs), enabling their promising applications in advanced fission and fusion energy systems. This perspective provides a comprehensive overview of radiation damage behavior reported in the literature to understand the fundamental mechanisms related to the impact of multi-principal metal components on phase stability, irradiation-induced defect clusters, irradiation hardening, and thermal conductivity of compositionally complex carbides. Several future research directions are recommended to critically evaluate the feasibility of designing and developing new ceramic materials for extreme environments using the transformative “multi-principal component” concept. Compared to the existing materials for nuclear applications including stainless steels, nickel alloys, ZrC, SiC, and potentially high-entropy alloys, as well as certain other compositionally complex ceramic families. CCCs appear to be more resistant to amorphization, growth of irradiation defect clusters, and void swelling.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Investigation of lasing characteristics of 1% Nd : YAG laser ceramics

The lasing characteristics of 1 % Nd : YAG laser ceramics synthesised at the Institute of Electrophysics, Ural Branch, Russian Academy of Sciences are studied. CW lasing is obtained in all the samples with the slope and total optical efficiencies of 25 % and 18 %, respectively. Intrinsic absorption and scattering losses in the ceramics are estimated. (extreme light fields and their applications)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Structure of crystalline oxide ceramics studied by phonon spectroscopy

This paper describes a method for gaining detailed insight into the structure and phonon spectrum of polycrystalline oxide ceramics. We examine how the diffusion coefficient of subterahertz phonons is related to the properties of a system of grain boundaries and to the grain size and structure and demonstrate that the temperature dependence of the phonon diffusion coefficient at liquid-helium temperatures is determined by the spectral properties of the intergranular layer, which allows one to estimate the volumeaveraged intergranular layer thickness and acoustic impedance. We also analyse the effect of plastic deformation via twinning on the formation of the structure of grains and intergranular layers, which determine the thermophysical, acoustic and optical properties of ceramic materials. (extreme light fields and their applications)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Nanopowders M{sub 2}O{sub 3} (M = Y, La, Yb, Nd) with spherical particles and laser ceramics based on them

We have considered the problems of agglomeration of yttrium aluminium garnet (YAG) nanopowders prepared by chemical co-precipitation of precursors from aqueous solutions and subsequent calcination. To fabricate YAG and Y{sub 2}O{sub 3} laser ceramic samples with high optical transmittance and reproducible characteristics, we have developed a method for producing non-agglomerated nanopowders of pure and doped Y{sub 2}O{sub 3} by homogeneous chemical precipitation. Nanopowders Y{sub 2}O{sub 3} with La and Yb as well as mixtures of Y{sub 2}O{sub 3} : Nd and several commercial nanopowders of aluminium oxide have been compacted; optimised compacting technique have been selected; ceramic samples (Y, La, Yb){sub 2}O{sub 3} and YAG : Nd with high optical transmittance at a wavelength of 1 {mu}m have been produced by solid-phase synthesis. (extreme light fields and their applications)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Multiwatt lasing of Nd:YAG laser ceramics containing 0.8% and 1% of Nd

The lasing characteristics of 1% Nd:YAG and 0.8% Nd:YAG laser ceramics synthesised, respectively, at the Institute of Electrophysics, Ural Branch, Russian Academy of Sciences and at the Institute of Radio Engineering and Electronics, Fryazino Branch, Russian Academy of Sciences are studied. Lasing was obtained in all the samples with a slope efficiency from 7% to 25% and a maximum output power exceeding 4 W. Intrinsic absorption and scattering losses in the ceramics are estimated. (extreme light fields and their applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Measurement of energy spectra of small-angle scattering and distribution of optical microinhomogeneities in laser ceramics

The energy spectra of small-angle light scattering from the samples of Nd:YAG ceramics and the spatial distributions of optical microinhomogeneities in them are measured. The spatial profiles of microinhomogeneities are found using the collinear heterodyne microprobe technique. Based on the obtained data, the comparison of noise and lasing characteristics of foreign and domestic samples of laser ceramics is carried out. (extreme light fields and their applications)

36 MATERIALS SCIENCE↗
DOE OSTI2015

Highly sensitive nonlinear luminescent ceramics for volumetric and multilayer data carriers

The interaction of optical ceramics based on wide-bandgap crystals with near-IR femtosecond laser radiation is studied experimentally. The formation of luminescent centres in LiF and MgF{sub 2} ceramics under the action of single laser pulses is considered. Two interaction regimes are used. In the regime of low-aperture focusing of laser radiation (800 nm, 30 fs, 0.3 mJ), multiple selffocusing and filamentation in the samples are observed. The luminescent centres are formed in thin channels induced by light filaments. The average effective self-focusing length is ∼100 μm; the formation of luminescent centres begins at this length and ceases at a wavelength of about 380 mm. The luminescent trace (spur) induced by a single laser filament was ∼30 μm long and 1.3 μm in diameter. The second regime of light interaction with the sample was based on high-aperture focusing with a simultaneous decrease in the laser pulse energy. This led to the formation of single pits with a diameter smaller than the optical diffraction limit. The luminescent centres induced by the laser radiation were aggregated colour centres. The mechanism of their creation included the highly-nonlinear generation of electron – hole pairs in the filamentation region, their recombination with the formation of anion excitons and the decay of excitons into Fresnel defects by the Lushchik – Vitol – Hersh – Pooley mechanism, as well as their recharging, migration and aggregation. (laser applications and other topics in quantum electronics)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Two-micron lasing on diode-pumped Y{sub 2}O{sub 3} : Tm ceramics

The results of investigation of the spectral, luminescent and lasing properties of Tm : Y{sub 2}O{sub 3} ceramics are presented. Lasing in Y{sub 2}O{sub 3} ceramics is obtained at wavelengths of 1.95 and 2.05 μm. The maximum output laser power at these wavelengths was 2.4 and 0.3 W, respectively. (lasers)

36 MATERIALS SCIENCE↗
DOE OSTI2016

Investigation of lasing characteristics of domestic Yb : YAG laser ceramics

We report on the synthesis and laser characteristics of Yb{sup 3+}-doped yttrium aluminium garnet (Y{sub 3}Al{sub 5}O{sub 12}) optical ceramics. The ceramics was produced by solid-phase reactive sintering of a mixture of Yb (5 at %) : Y{sub 2}O{sub 3} and Al{sub 2}O{sub 3} nanopowders synthesised by laser ablation, using additional calcination of the mixture before compaction. In a thin disk geometry, multiwatt laser oscillation was obtained at a wavelength of 1030 nm with a power of 5.2 W and a slope efficiency of 37.0% at a pump pulse period-toduration ratio of 5.72. (lasers)

36 MATERIALS SCIENCE↗
DOE OSTI2018

Continuous-wave 80-W lasing in Yb : YAG ceramics

We report on continuous-wave lasing at a wavelength of 1030 nm with a maximum power of 80 W and a slope efficiency of 26% in a thin disk element made of domestic ytterbium-doped yttrium – aluminium – garnet ceramics [(Yb{sub 0.05}Y{sub 0.95}){sub 3}Al{sub 5}O{sub 12}]. The studied ceramic sample was fabricated by solid-phase sintering of a mixture of (Yb{sub 0.05}Y{sub 0.95}){sub 2}O{sub 3} and Al{sub 2}O{sub 3} nanopowders synthesised by laser ablation. The measured laser characteristics in cw and repetitively pulsed regimes are presented. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Determination of specific losses in highly transparent Nd : YAG ceramics by laser calorimetry

Specific absorption losses in five samples of (1% – 4%) Nd : YAG optical ceramics are measured by laser calorimetry. The measurement results show that the specific losses increase from 7 × 10{sup −3} to 13 × 10{sup −3} cm{sup −1} as the neodymium concentration increases above 2 at%. The principal possibility of separate determination of scattering and absorption losses using additional measurements of total losses in ceramic material is shown. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Beta Radiation Hardness of GYGAG(Ce) Transparent Ceramic Scintillators

GYGAG(Ce) transparent ceramic garnet scintillators were irradiated with electrons from 0.5 to 2 MeV with fluences from 10 16 e – /cm 2 to 10 19 e – /cm 2 , corresponding to doses from 0.3 to 310 Gigarad. Absorption spectra were measured before and after irradiations. Light yields from alpha, beta, and gamma excitations were measured before and after irradiation and compared to preirradiation values to gain a deeper understanding of how electron irradiations can affect light yield, as well as defects generated in both the surface and bulk. Within experimental error, no degradation in light yield was observed for the electron-irradiated samples, as measured via beta or gamma excitation, with minimal degradation observed via alpha excitation. A small increase in optical absorption near the wavelength of emission was observed following the largest dose irradiation. These results suggest that GYGAG(Ce) is radiation hard to electron irradiation up to 10 19 e – /cm 2 and doses up to 310 Gigarad. Furthermore, this robustness to irradiation indicates that transparent ceramic garnets may prove useful for applications such as scintillation-based nuclear batteries by allowing for higher energy beta emitters, increased power densities, and enabling long service lifetimes.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Thermophysical Properties of Multiphase Borosilicate Glass-Ceramic Waste Forms

Multiphase borosilicate glass-ceramics represent one candidate to contain radioactive nuclear waste separated from used nuclear fuel. In this work, the thermophysical properties from room temperature to 1273 K were investigated for four different borosilicate glass-ceramic compositions containing waste loadings from 42 to 60 wt% to determine the sensitivity of these properties to waste loading, as-fabricated microstructure, and potential evolutions in microstructure brought about by temperature transients. The thermal expansion, specific heat capacity, thermal diffusivity, and thermal conductivity are presented. The impact of increasing waste loading is shown to have a small but measurable effect on the thermophysical properties between the four compositions, contrasted to a much greater impact observed when transitioning from predominantly crystalline to amorphous systems. Thermal cycling below 1273 K was not found to measurably impact the thermophysical properties of the compositions investigated here.

Glass Ceramic↗
DOE OSTI2016

Sealing glass-ceramics with near linear thermal strain, Part II: Sequence of crystallization and phase stability

Here, the sequence of crystallization in a re-crystallizable lithium silicate sealing glass-ceramic Li 2 O-SiO 2 -Al 2 O 3 -K 2 O-B 2 O 3 -P 2 O 5 -ZnO was analyzed by in situ high temperature X-ray diffraction (HTXRD). Glass-ceramic specimens have been subjected to a 2-stage heat treatment schedule, including rapid cooling from sealing temperature to a 1st hold temperature 650 °C, following by heating to a 2nd hold temperature of 810 °C. Notable growth and saturation of Quartz was observed at 650 °C (1st hold).

36 MATERIALS SCIENCE↗