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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

EPR and magnetic susceptibility investigation of iron-zinc-phosphate glass ceramics

(Fe{sub 2}O{sub 3}){sub x}⋅(P{sub 2}O{sub 5}){sub 40}⋅(ZnO){sub 60−x} glass ceramics containing different concentrations of Fe{sub 2}O{sub 3} ranging from 1 to 20 mol% were obtained by heat treatment of glass samples at 650 °C for 2 h. The structural and magnetic properties of these glass ceramics were investigated by means of electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. The EPR spectra of the studied samples revealed absorptions centered at g ≈ 2.0 and 4.3. The compositional variations of the intensity and line width of these absorption lines was interpreted in terms of the variation in Fe{sup 3+} and Fe{sup 2+} ions concentration in the glass ceramics as well as the interaction between the iron ions. The magnetic susceptibility data evidenced the presence of both Fe{sup 3+} and Fe{sup 2+} ions, with their relative content depending on the Fe{sub 2}O{sub 3} concentration. Dipolar and superexchange interactions involving iron ions were revealed depending on the iron content of the sample.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Room temperature strain rate sensitivity in precursor derived HfO{sub 2}/Si-C-N(O) ceramic nanocomposites

Investigation on the room temperature strain rate sensitivity using depth sensing nanoindentation is carried out on precursor derived HfO{sub 2}/Si-C-N(O) ceramic nanocomposite sintered using pulsed electric current sintering. Using constant load method the strain rate sensitivity values are estimated. Lower strain rate sensitivity of ∼ 3.7 × 10{sup −3} is observed and the limited strain rate sensitivity of these ceramic nanocomposites is explained in terms of cluster model. It is concluded that presence of amorphous Si-C-N(O) clusters are responsible for the limited flowability in these ceramics.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electrical conductivity anomaly and X-ray photoelectron spectroscopy investigation of YCr{sub 1−x}Mn{sub x}O{sub 3} negative temperature coefficient ceramics

Electrical conductivity anomaly of perovskite-type YCr{sub 1−x}Mn{sub x}O{sub 3} negative temperature coefficient (NTC) ceramics produced by spark plasma sintering (SPS) has been investigated by using defect chemistry theory combination with X-ray photoelectron spectroscopy (XPS) analysis. From the results of the lnρ-1/T curves and the XPS analysis, it can be considered that YCr{sub 1−x}Mn{sub x}O{sub 3} ceramics exhibit the hopping conductivity. The major carriers in YCrO{sub 3} are holes, which are compensated by the oxygen vacancies produced due to the introduction of Mn ions. The Mn{sup 4+} ion contents increase monotonically in the range of 0.2 ≤ x ≤ 0.5. The resistivity increases at first and then decreases with increasing Mn contents, which has the same varying tendency with activation energy. The electrical conductivity anomaly appearing in these ceramics may be due to the variation of Cr{sup 4+} and Mn{sup 4+} ions concentration as Mn content changes.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Dual-enhancement of ferro-/piezoelectric and photoluminescent performance in Pr{sup 3+} doped (K{sub 0.5}Na{sub 0.5})NbO{sub 3} lead-free ceramics

A mutual enhancement action between the ferro-/piezoelectric polarization and the photoluminescent performance of rare earth Pr{sup 3+} doped (K{sub 0.5}Na{sub 0.5})NbO{sub 3} (KNN) lead-free ceramics is reported. After Pr{sup 3+} doping, the KNN ceramics exhibit the maximum enhancement of ∼1.2 times in the ferroelectric remanent polarization strength and ∼1.25 times in the piezoelectric coefficient d{sub 33}, respectively. Furthermore, after undergoing a ferro-/piezoelectric polarization treatment, the maximum enhancement of ∼1.3 times in photoluminescence (PL) was observed in the poled 0.3% Pr{sup 3+} doped sample. After the trivalent Pr{sup 3+} unequivalently substituting the univalent (K{sub 0.5}Na{sub 0.5}){sup +}, A-sites ionic vacancies will occur to maintain charge neutrality, which may reduce the inner stress and ease the domain wall motions, yielding to the enhancement in ferro-/piezoelectric performance. The polarization-induced enhancement in PL is attributed to the decrease of crystal symmetry abound the Pr{sup 3+} ions after polarization. The dual-enhancement of the ferro-/piezoelectric and photoluminescent performance makes the Pr{sup 3+} doped KNN ceramic hopeful for piezoelectric/luminescent multifunctional devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The emergence of magnetic properties in (Pb{sub 0.845}Sm{sub 0.08}Fe{sub 0.035})(Ti{sub 0.98}Mn{sub 0.02})O{sub 3} and (Pb{sub 0.88}Nd{sub 0.08})(Ti{sub 0.98}Mn{sub 0.02})O{sub 3} perovskite ceramics

The emergence of magnetic properties and quadratic magnetoelectric coupling in a material with outstanding ferroelectric properties has been pursued. Thus, the multiferroicity driven by the substitution of rare earth R{sup 3+} ions (R = Sm, Nd) on the A-site of PbTiO{sub 3} perovskite ceramics has been investigated. In some samples, a transition element with large ionic radius, like Fe{sup 2+}, has been also added on the A site. Polycrystalline ceramic samples with composition (Pb{sub 1-3x/2-y}R{sub x}Fe{sub y}) (Ti{sub 0.98}Mn{sub 0.02})O{sub 3} (R = Sm; x = 0.08, y = 0.035) and (Pb{sub 1−3x/2}R{sub x})(Ti{sub 0.98}Mn{sub 0.02})O{sub 3} (R = Nd, x = 0.08) have been prepared by conventional solid state ceramic processing, starting from reagent grade oxide powders. X-ray diffraction analysis confirmed the obtaining of a crystalline phase with tetragonal P4 mm symmetry. Transmission electron microscopy and high resolution transmission electron microscopy investigations have been carried out in order to analyze the local structure. Temperature dependence of dielectric permittivity revealed a strong anomaly at the temperature T{sub c} of the paraelectric-ferroelectric phase transition. Transition temperature values depend on the R ion type and are lower than in pure lead titanate by 80–100 K. A broad anomaly of dielectric permittivity is found below 140–180 K, where magnetization also increases due to the quadratic magnetoelectric coupling between ferroelectric and magnetic states. For the (Pb{sub 0.845}Sm{sub 0.08}Fe{sub 0.035})(Ti{sub 0.98}Mn{sub 0.02})O{sub 3} composition, the piezoelectric charge coefficient at room temperature was d{sub 31} ∼−6.5 pC/N and the remanent magnetization M{sub r} at room temperature was about 0.1 emu/g.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A quantitative acoustic emission study on fracture processes in ceramics based on wavelet packet decomposition

We base a quantitative acoustic emission (AE) study on fracture processes in alumina ceramics on wavelet packet decomposition and AE source location. According to the frequency characteristics, as well as energy and ringdown counts of AE, the fracture process is divided into four stages: crack closure, nucleation, development, and critical failure. Each of the AE signals is decomposed by a 2-level wavelet package decomposition into four different (from-low-to-high) frequency bands (AA{sub 2}, AD{sub 2}, DA{sub 2}, and DD{sub 2}). The energy eigenvalues P{sub 0}, P{sub 1}, P{sub 2}, and P{sub 3} corresponding to these four frequency bands are calculated. By analyzing changes in P{sub 0} and P{sub 3} in the four stages, we determine the inverse relationship between AE frequency and the crack source size during ceramic fracture. AE signals with regard to crack nucleation can be expressed when P{sub 0} is less than 5 and P{sub 3} more than 60; whereas AE signals with regard to dangerous crack propagation can be expressed when more than 92% of P{sub 0} is greater than 4, and more than 95% of P{sub 3} is less than 45. Geiger location algorithm is used to locate AE sources and cracks in the sample. The results of this location algorithm are consistent with the positions of fractures in the sample when observed under a scanning electronic microscope; thus the locations of fractures located with Geiger's method can reflect the fracture process. The stage division by location results is in a good agreement with the division based on AE frequency characteristics. We find that both wavelet package decomposition and Geiger's AE source locations are suitable for the identification of the evolutionary process of cracks in alumina ceramics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Ferroic characterizations, phase transformation, and internal bias field in 0.75Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3}–0.25PbTiO{sub 3} multiferroic ceramic

The complex perovskite of 0.75Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3}–0.25PbTiO{sub 3} (0.75PFW-0.25PT) ceramic was prepared by the conventional oxide mixing method. The detailed microstructure of 0.75PFW-0.25PT ceramic was investigated. At room temperature, the TEM analysis reveals that only cubic structure (nonpolar) exists, which is different from the phase coexistence of cubic (66%) and tetragonal (34%) structure revealed by XRD. A mechanism dominated by a temperature rise due to electron-beam irradiation has been proposed. The XPS measurement confirms the mixed balance state of Fe{sup 2+} and Fe{sup 3+} in the as-prepared 0.75PFW-0.25PT specimen, which facilitates the formation of the defect dipoles with oxygen vacancies, in turn resulting in the internal-bias field (E{sub i}) phenomenon. The appearance of weak magnetic interactions is believed relating to the presence of noncompensated magnetic moments in Fe-rich islands. These results provide key information for understanding the composition, defect, ferroelectric, and ferromagnetic properties in 0.75PFW-0.25PT ceramic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Impedance spectroscopic characterization of gadolinium substituted cobalt ferrite ceramics

Gadolinium (Gd) substituted cobalt ferrites (CoFe{sub 2−x}Gd{sub x}O{sub 4}, referred to CFGO) with variable Gd content (x = 0.0–0.4) have been synthesized by solid state ceramic method. The crystal structure and impedance properties of CFGO compounds have been evaluated. X-ray diffraction measurements indicate that CFGO crystallize in the inverse spinel phase. The CFGO compounds exhibit lattice expansion due to substitution of larger Gd ions into the crystal lattice. Impedance spectroscopy analysis was performed under a wide range of frequency (f = 20 Hz–1 MHz) and temperature (T = 303–573 K). Electrical properties of Gd incorporated Co ferrite ceramics are enhanced compared to pure CoFe{sub 2}O{sub 4} due to the lattice distortion. Impedance spectroscopic analysis illustrates the variation of bulk grain and grain-boundary contributions towards the electrical resistance and capacitance of CFGO materials with temperature. A two-layer heterogeneous model consisting of moderately conducting grain interior (ferrite-phase) regions separated by insulating grain boundaries (resistive-phase) accurately account for the observed temperature and frequency dependent electrical characteristic of CFGO ceramics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Dielectric investigations of polycrystalline samarium bismuth ferrite ceramic

Results of broadband dielectric investigations of samarium doped bismuth ferrite ceramics are presented in wide temperature range (20–800 K). At temperatures higher than 400 K, the dielectric properties of samarium bismuth ferrite ceramics are governed by Maxwell-Wagner relaxation and electrical conductivity. The DC conductivity increases and activation energy decreases with samarium concentration. In samarium doped bismuth ferrite, the ferroelectric phase transition temperature decreases with samarium concentration and finally no ferroelectric order is observed at x = 0.2. At lower temperatures, the dielectric properties of ferroelectric samarium doped bismuth ferrite are governed by ferroelectric domains dynamics. Ceramics with x = 0.2 exhibit the relaxor-like behaviour.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Phase characteristics of 0.92Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-0.08BiAlO{sub 3} ceramics

The phase characteristics of 0.92Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-0.08BiAlO{sub 3} lead-free ceramics were investigated systematically. The loss tangent of poled sample shows a broad peak when heating to about 80 °C, i.e., depolarization temperature T{sub d}. The polarization-electric field hysteresis loops at different temperature exhibit the feature of ferroelectric (FE)- antiferroelectric (AFE) phase transition and the co-existence of FE and AFE phase. The pyroelectric coefficients curve confirms its diffusion behaviors. The initial hysteresis loop and switching current curves under T{sub d} indicate the co-existence of FE and AFE phase. The domain morphology of transmission electron microscopy supports the co-existence of FE and AFE phase. Our work not only exhibit that the FE and AFE phase characteristics of 0.92Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-0.08BiAlO{sub 3} ceramics but also they may be helpful for further investigation on lead-free ceramics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Study of the structure and ferroelectric behavior of BaBi{sub 4-x}La{sub x}Ti{sub 4}O{sub 15} ceramics

The structure and ferroelectric properties of Lanthanum substituted barium bismuth titanate BaBi{sub 4-x}La{sub x}Ti{sub 4}O{sub 15} (0 ≤ x ≤ 0.5) ceramics prepared by solid-state reaction method have been investigated. X-ray diffraction (XRD) confirms the formation of a single phase material. The distribution of lanthanum into the perovskite layers and (Bi{sub 2}O{sub 2}){sup 2+} layers of BaBi{sub 4}Ti{sub 4}O{sub 15} ceramics have been revealed through Raman spectroscopy. At lower value of x, it is seen that La{sup 3+} ions prefer to substitute A-site Bi{sup 3+} ions in the perovskite layers while for higher x values, La{sup 3+} ions get incorporated into the (Bi{sub 2}O{sub 2}){sup 2+} layers. A critical La content of x ∼ 0.2 in BaBi{sub 4-x}La{sub x}Ti{sub 4}O{sub 15} is seen to exhibit a large remnant polarization (P{sub r}) with low coercive field (E{sub c}). The improvement in the ferroelectric properties of La substituted BaBi{sub 4}Ti{sub 4}O{sub 15} ceramics has been explained in terms of changing oxygen vacancy concentration and structural relaxation. Tunable ferroelectric materials can be obtained by manipulating the doping amount of lanthanum ion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Hybrid improper ferroelectricity in Ruddlesden-Popper Ca{sub 3}(Ti,Mn){sub 2}O{sub 7} ceramics

The hybrid improper ferroelectricity (HIF) has been proposed as a promising way to create multiferroic materials with strong magnetoelectric coupling by the first-principle calculation, and the experimental evidences of HIF in Ruddlesden-Poper Ca{sub 3}(Ti{sub 1−x}Mn{sub x}){sub 2}O{sub 7} (x = 0, 0.05, 0.1, and 0.15) ceramics have been shown in the present work. The room temperature ferroelectric hysteresis loops are observed in these ceramics, and a polar orthorhombic structure with two oxygen tilting modes has been confirmed by the X-ray powder diffraction. A first-order phase transition around 1100 K in Ca{sub 3}Ti{sub 2}O{sub 7} was evidenced, and the temperatures of phase transitions decrease linearly with increasing of the contents of Mn{sup 4+} ions. Based on the result of first-principle calculations, the polarization should be reversed by switching through the mediated Amam phase in Ca{sub 3}Ti{sub 2}O{sub 7} ceramics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Thermotropic phase transitions in Pb{sub 1−x}Sr{sub x}(Al{sub 1/3}Nb{sub 2/3}){sub 0.1}(Zr{sub 0.52}Ti{sub 0.48}){sub 0.9}O{sub 3} ceramics: Temperature dependent dielectric permittivity and Raman scattering

The phase transitions of Pb{sub 1−x}Sr{sub x}(Al{sub 1/3}Nb{sub 2/3}){sub 0.1}(Zr{sub 0.52}Ti{sub 0.48}){sub 0.9}O{sub 3} (Sr-modified PAN-PZT) ceramics with Sr compositions of x = 2%, 5%, 10% and 15% have been investigated using X-ray diffraction (XRD), temperature dependent dielectric permittivity and Raman scattering. The XRD analysis show that the phase transition occurs between Sr composition of 5% and 10%. Based on the broad dielectric peaks at 100 Hz, the diffused phase transition from tetragonal (T) to cubic (C) structure shifts to lower temperature with increasing Sr composition. The dramatic changes of wavenumber and full width at half-maximum (FWHM) for E(TO{sub 4})′ softing mode can be observed at morphotropic phase boundary (MPB). Moreover, the MPB characteristic shows a wider and lower trend of temperature region with increasing Sr composition. It could be ascribed to the diminishment of the energy barrier and increment of A-cation entropy. Therefore, the Sr-modified PAN-PZT ceramics unambiguously undergo two successive structural transitions (rhombohedral-tetragonal-cubic phase) with temperature from 80 to 750 K. Correspondingly, the phase diagram of Sr-modified PAN-PZT ceramics can be well depicted.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Quantitative phase separation in multiferroic Bi{sub 0.88}Sm{sub 0.12}FeO{sub 3} ceramics via piezoresponse force microscopy

BiFeO{sub 3} (BFO) is a classical multiferroic material with both ferroelectric and magnetic ordering at room temperature. Doping of this material with rare-earth oxides was found to be an efficient way to enhance the otherwise low piezoelectric response of unmodified BFO ceramics. In this work, we studied two types of bulk Sm-modified BFO ceramics with compositions close to the morphotropic phase boundary (MPB) prepared by different solid-state processing methods. In both samples, coexistence of polar R3c and antipolar P{sub bam} phases was detected by conventional X-ray diffraction (XRD); the non-polar P{sub nma} or P{sub bnm} phase also has potential to be present due to the compositional proximity to the polar-to-non-polar phase boundary. Two approaches to separate the phases based on the piezoresponse force microscopy measurements have been proposed. The obtained fractions of the polar and non-polar/anti-polar phases were close to those determined by quantitative XRD analysis. The results thus reveal a useful method for quantitative determination of the phase composition in multi-phase ceramic systems, including the technologically most important MPB systems.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Chemical environment of rare earth ions in Ge{sub 28.125}Ga{sub 6.25}S{sub 65.625} glass-ceramics doped with Dy{sup 3+}

We have annealed Ge{sub 28.125}Ga{sub 6.25}S{sub 65.625} glasses doped with 0.5% Dy to create glass-ceramics in order to examine the local chemical environment of the rare earth ions (REI). More than 12 times enhancement of the emission at 2.9 and 3.5 μm was achieved in glass-ceramics produced using prolonged annealing time. Elemental mapping showed clear evidence that Ga{sub 2}S{sub 3} crystalline grains with a size of 50 nm were dispersed in a Ge-S glass matrix in the glass-ceramics, and the REI could only be found near the Ga{sub 2}S{sub 3} crystalline grains. From the unchanged lineshape of the emissions at 2.9 and 3.5 μm and lack of splitting of the absorption peaks, we concluded that the REI were bonded to Ga on the surface of the Ga{sub 2}S{sub 3} crystals.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Counter-intuitive experimental evidence on the initiation of radical crack in ceramic thin films at the atomic scale

The basic issue related to radial crack in ceramic thin films has received considerable attention due to the fact that the radial crack plays an important role in evaluating the toughness properties of ceramic materials. In this work, an atomic-scale new experimental evidence is clearly presented to reveal the counter-intuitive initiation, the nucleation and the propagation mechanism of the radial crack in Al-Cr-N ceramic thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effects of magnetic field treatment on dielectric properties of CCTO@Ni/PVDF composite with low concentration of ceramic fillers

Using melt mixing, we produced a ceramic/polymer composite with a matrix of polyvinylidene fluoride (PVDF) and a filler of 5 vol.% Ni-deposited CaCu{sub 3}Ti{sub 4}O{sub 12} core-shell ceramic particles (CCTO@Ni), and studied its prominent dielectric characteristics for the first. Its phase composition and morphology were analyzed by X-ray diffraction and scanning electron microscopy, respectively. After treating the composite films with various durations of a magnetic field treatment, we compared their dielectric properties. We found that the CCTO@Ni ceramic had a typical urchin-like core-shell structure, and that different durations of the magnetic field treatment produced different distributions of ceramic particles in the PVDF matrix. The dielectric permittivity of the untreated CCTO@Ni/PVDF composite was 20% higher than that of neat PVDF, and it had a low loss tangent. However, only the composite treated for 30 min in the magnetic field had an ultra-high dielectric permittivity of 1.41 × 10{sup 4} at 10 Hz, three orders of magnitude higher than the untreated composite, which declined dramatically with increasing frequency, accompanied by an insulating-conducting phase transition and an increase in loss tangent. Our results demonstrate that changes in the dielectric properties of PVDF composites with magnetic field treatment are closely related to the percolation effect and interfacial polarization.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Influence of temporary organic bond nature on the properties of compacts and ceramics

This work contains results of investigation of obtaining high thermally conductive ceramics from commercial powders of aluminum nitride and yttrium oxide by the method of monoaxial compaction of granulate. The principal scheme of preparation is proposed and technological properties of granulate are defined. Compaction conditions for simple items to use as heat removal in microelectronics and power electrical engineering have been established. Investigations of thermophysical properties of obtained ceramics and its structure by the XRD and SEM methods have been carried out. Ceramics with thermal conductivity from 172 to 174 W/m·K has been obtained as result of this work.

36 MATERIALS SCIENCE↗