Effect of Concentration of SH U 555A Labeled Human Melanoma Cells on MR Spin Echo and Gradient Echo Signal Decay at 0.2, 1.5, and 3T

In the current study the effect of increasing concentrations of superparamagnetic iron oxide labeled cells on the MRI signal decay at magnetic field strengths of 0.2, 1.5, and 3 T was evaluated. The spin echo and gradient echo cellular transverse relaxivity was systematically studied for various concentrations (N = 1, 5, 10, 20, 40, and 80 cells/μl_gel) of homogeneously suspended SH U 555A labeled SK-Mel28 human melanoma cells. For all field strengths investigated a linear relationship between cellular transverse relaxation enhancement and cell concentration was found. In the spin echo case, the cellular relaxivities [i.e., d(ΔR ₂)/dN] were determined to 0.12 s⁻¹ (cell/μl)⁻¹ at 0.2 T, 0.16 s⁻¹ (cell/μl)⁻¹ at 1.5 T, and 0.17 s⁻¹ (cell/μl) at 3 T. In the gradient echo case, the calculated cellular relaxivities (i.e., d(ΔR ₂ ^* )/dN) were 0.51 s⁻¹ (cell/μl)⁻¹ at 0.2 T, 0.69 s⁻¹ (cell/μl)⁻¹ at 1.5 T, and 0.71 s⁻¹ (cell/μl)⁻¹ at 3 T. The proposed preparation technique has proven to be a simple and reliable approach to quantify effects of magnetically labeled cells in vitro. On the basis of this quantification well suited tissue specific models can be derived.     

Diffusion-weighted imaging of the spine using radialk-space trajectories

Introduction Diffusion-weighted MR imaging (DWI) of the spine requires robust imaging methods, that are insensitive to susceptibility effects caused by the transition from bone to soft tissue and motion artifacts due to breathing, swallowing, and cardiac motion. The purpose of this study was to develop a robust imaging method suitable for DWI of the spine. Methods and subjects A radialk-space spin echo sequence has been implemented, which is sell-navigating because each acquisition line passes through the origin ofk-space. Influence of cardiac motion and associated flow of cerebrospinal fluid is minimized by cardiac gating with a finger photoplethysmograph. The sequence has been tested on a 1.5T system. Diffusion-weighted images of six normal volunteers were acquired in the sagittal plane with 4b values between 50 and 500 s mm⁻². Because of the symmetries of the cord, diffusion measurements in the head-foot (HF) or left-right (LR) directions were sufficient to measure the dominant effects of anisotropy. Results The apparent diffusion coefficients (ADCs) measured, respectively, in the LR and HF directions were (0.699 ± 0.050) × 10⁻³ and (1.805 ± 0.086) × 10⁻³ mm² s⁻¹ in the spinal cord. (1.588 ± 0.082) × 10⁻³ and (1.528 ± 0.052) × 10⁻³ mm² s⁻¹ in the intervertebral disks, and (0.346 ± 0.047) × 10⁻³ and (0.306 ± 0.035) × 10⁻³ mm² s⁻¹ in the vertebrae of the cervicothoraeic spine. Conclusion Diffusion-weighted spin echo sequences with radial trajectories ink-space provide a means of achieving robust, high quality diffusion-weighted imaging and measuring ADCs in the spine. The application of the diffusion-weighting gradients in different directions allows diffusion anisotropy to be measured.     

Fabrication,property and application of novel pyroelectric single crystals—PMN–PT

The pyroelectric properties and temperature stability of Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃(PMN–xPT) single crystals (0.13 ≤ × ≤ 0.40) were investigated. The best choice for pyroelectric performance is [111]-oriented PMN–0.26PT single crystal whose figures of merit for voltage responsivity and detectivity are 0.11 m²/C and 15 × 10⁻⁵ Pa^−1/2, respectively. However, the [001]-oriented PMN–0.37PT single crystal has much better temperature stability, whose temperature coefficient of pyroelectric property is 0.5%/K in the range of 20 °C to 55 °C, and Curie temperature is high: 175 °C. We also found that PMN–xPT possessed low thermal diffusivity D ~ 4.4 × 10⁻⁷ m²/s, low volume specific heat C _v~ 2.5 × 10⁶ J/m³ K and tunable permittivity ε ~ (300–7000). The pyroelectric performances of PMN–xPT single crystals are superior to those of conventional pyroelectric materials and promising for IR device applications.     

Tissue oxygen tension measurements in the Shionogi model of prostate cancer using 19 F MRS and MRI

Objectives: To investigate changes in tumour tissue oxygenation throughout the tumour growth–regression–relapse cycle in an androgen-dependent animal tumour model. Materials and methods: ¹⁹F T₁ relaxometry of Perfluoro-15-Crown-5-Ether was used to measure in vivo partial oxygen pressure (pO₂) of Shionogi tumours on a 2.35-T MR scanner. Perfluoro-15-Crown-5-Ether was administered as an emulsion injected intravenously or as a neat compound injected directly into the tumour. Non-localized, tumour ¹⁹F T₁ measurements, made at multiple time points throughout the tumour cycle, were translated into pO₂ levels. Results: No correlation between tumour size and pO₂ values was found. Values of pO₂ for growing tumours (50 ± 30 torr) were significantly lower than for regressing and relapsing tumours after 9 days post-castration (70 ± 10 torr, p<0.05). Maximum pO₂ values (90 ± 30 torr) were reached between fifth and eighth day post-castration, when tumour pO₂ was significantly higher than both pre-castration (p<0.001) and after 9 days post-castration (p<0.05). Conclusion: We demonstrate that longitudinal pO₂ measurements in vivo are feasible. Values of pO₂ for growing androgen-dependent tumours were significantly lower than for regressing and relapsing androgen-independent tumours. These results have potential clinical importance in optimizing the timing of chemotherapy and/or radiotherapy of hormone dependent tumours.     

Water self-diffusion tensor changes in an avian genetic developmental model of epilepsy

Diffusion tensor imaging (DTI) was used to investigate whether tissue anisotropy in the developing brain is modified by recurrent seizures in epileptic chickens. Twelve epileptic chickens were sorted equally into two experimental groups at 10 days old. Until the age of 180 days, one group was photically stimulated beginning at an age of 2 weeks and repeated every 2 days while the other group was not stimulated. The photic stimulation induced generalized tonic–clonic seizures, and the unstimulated group did not display seizures. Both treatment groups were imaged at three time points, 45 (juvenile), 90 (adolescent), and 180 (adult) days posthatching, and maps of major and minor elements of anisotropy (η and ε), trace and fractional anisotropy (FA) were generated. The η, ε, and trace values in the hyperstriatum, archistriatum, and optic tectum showed significant changes as a function of developmental time point. Differences and/or interactions due to seizures were seen in the archistriatum and optic tectum for η, ε, and trace with the largest differences between the stimulated and unstimulated birds being seen for η in juvenile birds in the archistriatum (38.1×10⁻¹¹ m²/s versus 18.0×10⁻¹¹ m²/s) and the optic tectum (53.9×10⁻¹¹ m²/s versus 27.1×10⁻¹¹ m²/s). With the DTI parameters being sensitive to microstructure in the brain, these results demonstrate that seizures produce measurable differences, over unstimulated chickens, in brain structure for juvenile chickens, but the differences disappear as the brain matures. In other words, while seizure activity appears to induce atypical biophysical change (relative to unseizing birds) in the brain at a young age, the change is apparently reversed as the brain matures.     

The C-neu mammary carcinoma in Oncomice; characterization and monitoring response to treatment with herceptin by magnetic resonance methods

To characterize spontaneously occurring c-neu/HER2 overexpressing tumours in oncomice and their response to herceptin by non-invasive magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI). Oncomice were monitored by localized ³¹P MRS during unperturbed growth and before and after treatment with 10 mg/kg herceptin (Hoffman La Roche) intraperitoneally for up to 21 days post-treatment. Vascular morphology and function was assessed by quantitation of tumour magnetic resonance (MR) relaxation rates R₂* and R₂ prior to and either during carbogen (95% O₂/5% CO₂) breathing or following administration of the blood-pool contrast agent NC100150 (Clariscan, Amersham Health). Immunohistochemistry showed strong membrane staining for HER2 protein overexpression. The ³¹P MRS showed only a significant (p<0.01) increase of phosphomonoester / total phosphate ratio over 21 days of growth. Herceptin increased the tumour volume doubling time compared to untreated tumours and significantly increased the phosphomonoester / -nucleoside triphosphate ratio 2 days after treatment (p=0.01). Tumours showed a highly heterogeneous yet significant (p<0.01) decrease or increase in R₂* in response to carbogen or NC100150 respectively. The absence of a decline in tumour bioenergetics with growth, commonly seen in ³¹P MRS studies of transplanted rodent tumour models, coupled with the heterogeneous blood volume revealed by ¹H MRI, suggest a metabolic and vascular phenotype similar to that found in human tumours.     

Thermoelectric properties of Bi and Cu co-doped Ca3Co2O6single crystals

Single crystals of Bi and Cu-doped Ca₃Co₂O₆were synthesized in a molten K₂CO₃flux. Using an obtained single crystal of (Ca_0.985(5)Bi_0.015(5))₃(Co_0.990(3)Cu_0.010(3))₂O₆elongated to the c-axis direction of the crystal structure, the electric resistivity (ρ) and Seebeck coefficient (S) were measured from room temperature to over 1000 K in air. The single crystal showed p-type semiconducting behavior with ρ values of 1.8 Ω cm at 303 K and 0.017 Ω cm at 1000 K. The S values were +254 μ VK^{− 1} at 325 K, +360 μ VK^{− 1} at 420 K, and +214 μ VK^{− 1} at 1000 K. The power factor (S ² ρ ^{− 1}) increased with an increase of temperature and attained 2.70 × 10^{− 4} Wm^{− 1}K^{− 2} at 1000 K.     

Synthesis and sintering properties of (La0.8Ca0.2−x Sr x )CrO3 perovskite materials for SOFC interconnect

Synthesis and sintering properties of the (La_0.8Ca_0.2−x Sr _x )CrO₃ samples doped by two alkaline earth metals in comparison to the doped only by one alkaline earth metal were evaluated by phase analysis, sintering properties, thermal expansion behaviors, and electrical conductivity. The sintered (La_0.8Ca_0.2−x Sr _x )CrO₃ (x = 0, 0.05, and 0.1) and (La_0.8Ca_0.2−x Sr _x )CrO₃ (x = 0.2) were found to have orthorhombic and rhombohedral symmetries, respectively. Relative density of the (La_0.8Sr_0.2)CrO₃ sample sintered at 1500^∘C for 5 h was lower than that of the (La_0.8Ca_0.2−x Sr _x )CrO₃ (x = 0, 0.05, and 0.1) sample. TECs of the (La_0.8Ca_0.2−x Sr _x )CrO₃ (x = 0, 0.05, 0.1, and 0.2) in air were 11 × 10⁻⁶/^∘C, 11.2 × 10⁻⁶/^∘C, 11.2 × 10⁻⁶/^∘C, and 11.3 × 10⁻⁶/^∘C, respectively. The electric conductivity of the (La_0.8Ca_0.2−x Sr _x )CrO₃ sample was determined.     

1H-NMRD and17O-NMR assessment of water exchange and rotational dynamics of two potential MRI agents: MP-1177 (an extracellular agent) and MP-2269 (a blood pool agent)

The parameters that govern water proton magnetic relaxation (e.g. water exchange rates, and rotational and electronic correlation times) of representatives of two classes of Gd(III) complexes have been estimated, using two different approaches and the results compared with those derived for known analogs. The complexes studied are: (i) the non-ionic GdDTPA-bis(methoxyethyl-amide) [Gd(DTPA-BMEA)], a typical small-molecule extracellular MR agent, and (ii) the ionic Gd(III) complex of 4-pentylbicyclo[2.2.2]octane-1-carboxyl-di-l-aspartyl-lysine-derived-DTPA [GdL]⁴⁻, a prototype MR blood pool agent, which binds to serum albumin in vivo through non-covalent hydrophobic interactions. An¹⁷O-NMR study of [Gd(DTPA-BMEA)] gives a water exchange rate constant ofk _ex ²⁹⁸ =(0.39±0.02)×10⁶ s⁻¹, identical to that for the bismethylamide analog [Gd(DTPA-BMA)]. Both approaches yield longer rotational correlation times for [Gd(DTPA-BMEA)], consistent with its higher molecular weight. An¹⁷O-NMR study of [GdL]⁴⁻ gives a water exchange rate constant ofk _ex ²⁹⁸ =(4.2±0.1)×10⁶ s⁻¹, identical to that for [Gd(DTPA)]²⁻. The water exchange rate on [GdL]⁴⁻ did not decrease considerably when bound to albumin, the lowest limit isk _ex,GdL-BSA=k _ex,GdL/2. Both approaches yield identical rotational correlation times for [GdL]⁴⁻, however, it was difficult to derive a consistent rotational constant for the albumin-bound [GdL]⁴⁻ using the different approaches (values ranged between 1.0 and 23.0 ns).     

Structural and electrical properties of low resistance Pt/Pd/Au contact on p-GaN

We have investigated electrical and structural properties of Pt/Pd/Au ohmic contact on p-type GaN:Mg (2.5 × 10¹⁷ cm⁻³) using Auger electron spectroscopy (AES) and glancing angle x-ray diffraction (GXRD) analysis. It was shown that the specific contact resistivity improved with increasing annealing temperature. The annealing of the contact at 600^∘C for 2 min in flowing N₂ atmosphere resulted in a specific contact resistivity of 3.1 × 10⁻⁵ Ω cm². Both GXRD and AES depth profile results show that Ga₃Pt₅, Ga₂Pd₅, and Au₇Ga₂ phases are formed at the interface region between metal and GaN when annealed at temperatures 600^∘C. Possible explanation is suggested to describe the annealing dependence of the specific contact resistivity of the Pt/Pd/Au contacts.     

High resolution SE-fMRI in humans at 3 and 7 T using a motor task

Object The sensitivity of spin echo (SE) experiments to blood oxygenation level dependent (BOLD) contrast was explored in a study of the same six subjects carried out at 3 and 7 T. Materials and methods Multi-slice, single shot, spin echo, echo planar images with a voxel size of 1 × 1 × 3 mm³ were acquired at three different echo times, during execution of a simple motor task. Results Significant activation was observed at all echo times at both field strengths. Analysis of the fractional signal change as a function of echo time indicated that the change in relaxation rate, ΔR ₂, at 7 T was −0.51 ± 0.14 s ⁻¹, which was 1.3 times larger than the value found at 3 T. Measurements of the percentage signal change on activation and temporal signal to noise ratio showed that there was an increase in the BOLD contrast to noise ratio (CNR) at 7 versus 3 T by a factor of 1.9. There was no overlap of areas of significant activation in the SE data acquired at either field strength with the site of large veins. Conclusion SE-BOLD CNR in motor cortex was found to increase significantly at 7 T compared with 3 T.     

Conductivity and expansion at high temperature in Sr0.7La0.3TiO3−α prepared under reducing atmosphere

Sr_0.7La_0.3TiO_3−α specimens were prepared in reducing atmosphere, and the structural and electrical properties were studied. The lattice parameter of Sr_0.7La_0.3TiO_3−α at room temperature was larger than that expected from Vegard’s law between SrTiO₃ and LaTiO₃ due to the reductive expansion. The conductivity of this specimen was 100 S cm⁻¹ at 1000°C, p_O2 = 10⁻¹³ Pa. However, the conductivity was not preserved after an oxidation-reduction cycle. Over p_O2 = 10² Pa, the conductivity drastically dropped with increasing p_O2. The thermal expansion coefficient of Sr_0.7La_0.3TiO_3−α was 11.8 × 10⁻⁶ K⁻¹ in 9% H₂/N₂ (room temperature – 1000°C). In this Sr_0.7La_0.3TiO_3−α, the chemical expansion on oxidation reached Δl/l_o = 0.51%, when changing p_O2 from 10⁻¹¹ Pa to 2 × 10⁴ Pa (air) at 1000°C.     

Effects of ZnO on the piezoelectric properties of Pb (Mn1/3 Sb 2/3 )O 3 -Pb(Zr,Ti)O 3 Ceramics

Perovskite-types 0.05Pb(Mn_1/3Sb_2/3)O₂-0.95Pb- (Zr_0.5Ti_0.5)O₃ (PMS-PZT) was synthesized by conventional bulk ceramic processing technique. ZnO as a dopant up to 0.5 mol% was incorporated into the PMS-PZT system, and the effects on piezoelectric properties were investigated. Pyrochlore phase was not detected to form during the synthesis of the PMS-PZT system with 0–0.5 mol% ZnO addition. The highest density of 7.92 g/cm³ was obtained when sintered at 1200^∘C for 2 h. Piezoelectric properties as a function of ZnO content were evaluated using a gain phase analyzer. Piezoelectric charge constant (d ₃₁) and piezoelectric voltage output coefficient (g ₃₁) increased up to −130 pC/N and −24.9 × 10³Vm/N, respectively, with increasing ZnO content. Mechanical quality factor (Q _m) was shown to reduce considerably with increasing ZnO content. When 0.3 mol% of ZnO was added into the system, electromechanical coupling factor (k _p) and relative dielectric constant (ε₃₃ ^T /ε_o) reached to the maximum of 56% and 1727, respectively.     

Standardized MR protocol for the evaluation of MRA sequences and/or contrast agents effects in high-degree arterial stenosis analysis

Purpose To investigate the relative role of high resolution (spatial or temporal) magnetic resonance angiography (MRA) sequence and of contrast agent properties in the evaluation of high-degree arterial stenosis. Methods We qualitatively and quantitatively studied both 50 and 95% (300 μm diameter) stenosis of a 6 mm arterial phantom with two contrast agents (CA), Gd-DOTA (r₁ =2.9 mM⁻¹ s⁻¹) versus P760 (r₁ =25 mM⁻¹ s⁻¹) at several CA concentrations, including arterial peak concentration after injection of either a single or double dose of CA, using either a high temporal (booster) or high spatial (HR) resolution 3D MRA sequences. Experimental data were then compared to theoretical data. Results With the 3D HR sequence, both visual and quantitative analysis were significantly better compared to the 3D booster sequence, at each phantom diameter. Quantitative analysis was significantly improved by injection of a double versus a single dose of each CA (Gd-DOTA or P760), primarily in high degree stenosis. Conclusion Combined MRA spatial resolution and high CA efficiency are mandatory to correctly evaluate high degree stenosis.     

Electrical properties of ultrathin HfO2 gate dielectrics on partially strain compensated SiGeC/Si heterostructures

Ultrathin HfO₂ gate dielectrics have been deposited on strained Si_0.69Ge_0.3C_0.01 layers by rf magnetron sputtering. The polycrystalline HfO₂ film with a physical thickness of ∼6.5 nm and an amorphous interfacial layer with a physical thickness of ∼2.5 nm have been observed by high resolution transmission electron microscopy (HRTEM). The electrical properties have been studied using metal-oxide-semiconductor (MOS) structures. The fabricated MOS capacitors on Si_0.69 Ge_0.3C_0.01 show an equivalent oxide thickness (EOT) of 2.9 nm, with a low leakage current density of ∼4.5 × 10 ^{− 7} A/cm² at a gate voltage of –1.0 V. The fixed oxide charge and interface state densities are calculated to be 1.9 × 10¹² cm^{− 2} and 3.3 × 10 ¹¹ cm^{− 2}eV⁻¹, respectively. The temperature dependent gate leakage characteristics has been studied to establish the current transport mechanism in high-k HfO₂ gate dielectric to be Poole–Frenkel one. An improvement in electrical properties of HfO₂ gate dielectrics has been observed after post deposition annealing in O₂ and N₂ environments.     

Hydrogenation induced transformation of paramagnetism to room-temperature ferromagnetism in co-doped TiO2 ceramics

Effects of Co _x Ti _1−x O _2−δ on the sinterability and the ferromagnetism properties of Co ₂sO ₃/TiO ₂ (0.0 < x < 0.06) ceramics are investigated in this paper. It is found that the Co-doped Ti O ₂ ceramics transform from paramagnetism to room-temperature ferromagnetism (RTFM) after hydrogenation. With annealing temperatures at 600^∘ C and 1000^∘ C, these as-prepared samples present anatase and rutile structures respectively, which are analyzed with X-ray diffraction (XRD). After hydrogenation, the relation between temperature variations and the magnetic susceptibility for the hydrogenated samples were measured under zero-field-cooled and field-cooled conditions by using SQUID magnetometer. And the hysteresis loops are observed. These ferromagnetism resonance data suggest that the observed RTFM is at least partly due to the Cobalt nano-particles in our hydrogenated samples.     

Study of bulk and grain-boundary conductivity of Ln<Subscript>2+x</Subscript>Hf<Subscript>2−x</Subscript>O<Subscript>7−δ</Subscript> (Ln = Sm-Gd; x = 0, 0.096) pyrochlores

The electrical conductivity of new solid electrolytes Eu_2.096Hf_1.904O_6.952 and Gd₂Hf₂O₇ have been compared with those for different pyrochlores including titanates and zirconates Ln_2+xМ_2−xO_7−δ (Ln = Sm-Lu; M = Ti, Zr; x = 0−0.81). Impedance spectroscopy data demonstrate that Eu_2.096Hf_1.904O_6.952 and Gd₂Hf₂O₇ synthesized from mechanically activated oxides have high ionic conductivity, comparable to that of their zirconate analogues. The bulk and grain-boundary components of conductivity in Sm_2.096Hf_1.904O_6.952 (Т_synth = 1600oС), Eu_2.096Hf_1.904O_6.952 and Gd₂Hf₂O₇ (Т_synth = 1670oС) have been determined. The highest bulk conductivity is offered by the disordered pyrochlores prepared at 1600oC and 1670oC: ~1.5 × 10⁻⁴ S/cm for Sm_2.096Hf_1.904O_6.952, 5 × 10⁻³ S/cm for Eu_2.096Hf_1.904O_6.952 and 3 × 10⁻³ S/cm for Gd₂Hf₂O₇ at 780oС, respectively. The conductivity of the fluorite-like phases at the phase boundaries of the Ln_2+xМ_2−xO_7−δ (Ln = Eu, Gd; M = Zr, Hf; x ~ 0.286) solid solutions, as well as that of the high-temperature fluorite-like phases Ln_2+xМ_2−xO_7−δ (Ln = Eu, Gd; M = Zr, Hf; x = 0−0.286), is lower than the conductivity of the disordered pyrochlores Ln_2+xМ_2−xO_7−δ (Ln = Eu, Gd; M = Zr, Hf; x = 0−0.096).     

Oxygen permeation properties and surface modification of acceptor-doped CeO2/MnFe2O4 composites

The preparation and oxygen permeation properties of the (Ce_0.8Pr_0.2)O_2−δ − x vol% MnFe₂O₄ composites, where x = 0 to 35, have been investigated. The samples were prepared by the Pechini method. In the case of Ce_0.8Pr_0.2O_2−δ, an oxygen flux density of 6 μmol⋅cm⁻²⋅s⁻¹ (L = 0.0247 cm) and the maximum methane conversion of 50% were attained at 1000^∘C. Unlike composites consisting of Gd-doped CeO₂ and MnFe₂O₄, the oxygen permeability of the (Ce_0.8Pr_0.2)O_2−δ – x vol% MnFe₂O₄ composites was almost constant regardless of the volume fraction of MnFe₂O₄; however, the optimum volume fraction of MnFe₂O₄ was determined to be 5 to 25 in the context of the chemical and mechanical stabilities under methane conversion atmosphere. In addition, the surface modification of the (Ce_0.8Gd_0.2)O_2−δ – 15 vol% MnFe₂O₄ composite was performed by using the FePt nanoparticles. The catalyst loading of 2.8 mg/cm² on the both side of the 0.3 mm-thick (Ce_0.8Gd_0.2)O_2−δ – 15vol% MnFe₂O₄ composite increased the oxygen flux density from 0.30 to 0.76 μmol⋅cm⁻²⋅s⁻¹ in the case of He/air gradients; however, the effect seems to be reduced in the case of high oxygen flux density caused by a large pO₂ gradient. Moreover, the Langmuir-Blodgett film of the FePt nanoparticles were successfully prepared on the tape-cast (Ce_0.8Gd_0.2)O_2−δ – 15vol% MnFe₂O₄ composite. Hydrophobic treatments for the surface of the composite were crucial to achieve high transfer ratio for the deposition of the LB film.     

Dispersion and rheology of BaTiO3 nanoparticles in ethanol–isopropanol solvents

Barium titanate (BaTiO₃) nanoparticles were dispersed in ethanol–isopropanol mixtures and their rheological behaviors were examined in terms of surfactant concentration (0–5 wt.% of the solids) and volumetric solids loading () over a shear-rate () range 1 to 1,000 s⁻¹. An oxyethylene-based polymeric surfactant was used to facilitate the nanoparticle dispersion. A pronounced viscosity reduction, >95% when compared to the suspensions without the dispersant, resulted with a surfactant concentration of 4 wt.% at a constant shear rate of 100 s⁻¹. This finding was in parallel with a simultaneous reduction in the mean “floc” size of the suspensions. Shear-thinning flow character resulted over most of the shear-rate range examined, especially for the concentrated suspensions with ϕ ≥ 0.25. The concentrated suspensions were indeed flocculated. This increased instability was partly due to the compression of electrical double layer as the particulate solids became more crowded in the carrier solvents, and also to the increased “effective” solids concentration because of the preferential adsorption of the surfactant molecules on the nanoparticle surface.     

Textured ferroelectric SrBi2Nb2O9 phase obtained by melt-quenching the SrBi2B2O7-Nb2O5 system and its anisotropic dielectric and pyroelectric properties

Textured SrBi₂Nb₂O₉ ceramics were obtained by quenching the melts of SrBi₂B₂O₇-Nb₂O₅ in equimolar ratio. The as-quenched samples were crystalline comprising 40% c-oriented grains. The influence of the post heat-treatment temperature on the orientation factor (f) and microstructure was studied using x-ray powder diffraction (XRD) and Scanning electron microscopy (SEM). The orientation factor was found to increase with increasing post heat-treatment temperature and reached a maximum value of 65% for the samples heated at 700°C for 10 h. Relative density and the grain-size of the partially grain oriented ceramics were found to increase with an increase in the heat-treatment temperature. The effect of texturing yielded anisotropy in the dielectric and pyroelectric properties. The dielectric constant ( e_r^￠ ( ^) = 114 ) \left( {\varepsilon_r^{\prime } \left( \bot \right) = 114} \right) and the pyroelectric coefficient (p(┴) = −0.07 nC cm⁻² °C⁻¹) along the direction perpendicular to the melt pressing axis were superior to that of the direction parallel ((e_r^￠ ( ||) = 93 \varepsilon_r^{\prime } \left( \parallel \right) = 93 ) (p(||) = −0.02 nC cm⁻² °C⁻¹)) (c-axis of the grain) to the pressing axis at room temperature.