Large Pr Research Articles

Structure and electrical properties of Bi0.5Na0.5TiO3-Y0.5Na0.5TiO3-BaTiO3 lead-free piezoelectric ceramics

New (1 – x − y)Bi0.5Na0.5TiO3-xY0.5Na0.5TiO3-yBaTiO3 lead-free ceramics have been prepared by a conventional ceramic fabrication technique, and their structure and electrical properties have been studied. A morphotropic phase boundary (MPB) of rhombohedral and tetragonal phases is formed at 0.04 < y < 0.10. As compared to pure Bi0.5Na0.5TiO3 ceramic, the partial substitutions of Y3+ for Bi3+ and Ba2+ for (Bi0.5Na0.5)2+ in the A-sites of Bi0.5Na0.5TiO3 lower effectively the coercive field E c and increase the remanent polarization P r of the ceramics. Because of low E c, large P r and the MPB, the ceramics with x = 0–0.02 and y = 0.06 exhibit the optimum piezoelectric properties: d 33 = 155–159 pC/N and k p = 28.8–36.7%. The temperature dependences of dielectric properties of the ceramics show relaxor-like behaviors. The ferroelectric properties at different temperature suggest that the ceramics may contain both the polar and non-polar regions near/above T d.

Structure, ferroelectric and piezoelectric properties of (Bi0.98−x La0.02Na1−x )0.5Ba x TiO3 lead-free ceramics

Lead-free (Bi0.98−x La0.02Na1−x )0.5Ba x TiO3 ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction show that La2+ and Ba2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.04<x<0.10. Compared with pure Bi0.5Na0.5TiO3 ceramics, the (Bi0.98−x La0.02Na1−x )0.5Ba x TiO3 ceramics possess much smaller coercive field E c and larger remanent polarization P r. Because of the low E c (3.38 kV/mm), large P r (46.2 μC/cm2) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x=0.06: d 33=181 pC/N and k p=36.3%. The depolarization temperature T d reaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both polar and non-polar regions at the temperatures above T d.

Prandtl-, Rayleigh-, and Rossby-Number Dependence of Heat Transport in Turbulent Rotating Rayleigh-Bénard Convection

Experimental and numerical data for the heat transfer as a function of the Rayleigh, Prandtl, and Rossby numbers in turbulent rotating Rayleigh-Bénard convection are presented. For relatively small Ra approximately 10(8) and large Pr modest rotation can enhance the heat transfer by up to 30%. At larger Ra there is less heat-transfer enhancement, and at small Pr less, similar 0.7 there is no heat-transfer enhancement at all. We suggest that the small-Pr behavior is due to the breakdown of the heat-transfer-enhancing Ekman pumping because of larger thermal diffusion.

Enhanced multiferroic properties of the high-valence Pr doped BiFeO3 thin film

High-valence Pr-doped BiFeO3 (BPF) multiferroic thin film was prepared by pulsed laser deposition on a Pt∕TiO2∕SiO2∕Si substrate. X-ray diffraction analysis indicates that the BPF film is of pure phase with a polycrystalline perovskite structure. The BPF film exhibited enhanced multiferroic properties: (i) a rectangular-shaped electric hysteresis loop with a large Pr of 75μC∕cm2 and a low Ec of 250kV∕cm at Emax ∼620kV∕cm, (ii) a saturated magnetic hysteresis loop with a large Ms of 58emu∕cm3, and (iii) a fatigue-free behavior after being subjected to 1.2×109 switching cycles, which were superior to, in some aspects, those of La- or Nd-doped BiFeO3 films reported before.

Structure, electrical properties and temperature characteristics of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Bi0.5Li0.5TiO3 lead-free piezoelectric ceramics

(1−x−y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3– yBi0.5Li0.5TiO3 lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique, and their structure, electrical properties, and temperature characteristics have been studied systematically. The ceramics can be well-sintered at 1050–1150 °C. The increase in K+ concentration decreases the grain-growth rate and promotes the formation of grains with a cubic shape, while the addition of Li+ decreases greatly the sintering temperature and assists in the densification of BNT-based ceramics. The results of XRD diffraction show that K+ and Li+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a solid solution with a pure perovskite structure. As x increases from 0.05 to 0.50, the ceramics transform gradually from rhombohedral phase to tetragonal phase and consequently a morphotropic phase boundary (MPB) is formed at 0.15≤x≤0.25. The concentration y of Li+ has no obvious influence on the crystal structure of the ceramics. Compared with pure Bi0.5Na0.5TiO3, the partial substitution of K+ and Li+ for Na+ lowers greatly the coercive field Ec and increases the remanent polarization Pr of the ceramics. Because of the MPB, lower Ec and large Pr, the piezoelectricity of the ceramics is improved significantly. For the ceramics with the compositions near the MPB (x=0.15–0.25 and y=0.05–0.10), the piezoelectric properties become optimum: piezoelectric coefficient d33=147–231 pC/N and planar electromechanical coupling factor kP=20.2–41.0%. In addition, the ceramics exhibit relaxor characteristic, which probably results from the cation disordering in the 12-fold coordination sites. The depolarization temperature Td shows a strong dependence on the concentration x of K+ and reaches the lowest values at the MPB. The temperature dependences of the ferroelectric and dielectric properties at high temperatures may imply that the ceramics may contain both the polar and non-polar regions at temperatures above Td.

Crystal Growth and Scintillation Properties of 2-Inch-Diameter ${\rm Pr}:{\rm Lu}_{3}{\rm Al}_{5} {\rm O} _{12}$ (Pr:LuAG) Single Crystal

In this work we tried to grow 2-inch-diameter and high quality Pr:LuAG single crystals by the Czochralski (Cz) method. To grow the large diameter Pr:LuAG single crystal, we have optimized growth conditions and the furnace design. As a result, we have succeeded in the growth of 2-inch-diameter Pr:LuAG single crystal with a length of 110 mm. To determine light yield and energy resolution the energy spectra were collected under 662 keV gamma-ray excitation (137Cs source) and detection by a photomultiplier (Hamamatsu H7826). The light yield was around three times higher than that of BGO and almost homogeneous with increasing solidification fraction up to 0.32. The energy resolution was around 8%. Furthermore, scintillation decay time was around 23 ns and almost homogeneous all over the crystal.

Piezoelectric and ferroelectric properties of (Bi0.94−xLaxNa0.94)0.5Ba0.06TiO3 lead-free ceramics

Lead-free piezoelectric ceramics (Bi0.94−x LaxNa0.94)0.5Ba0.06TiO3 have been fabricated by an ordinary sintering technique, and their piezoelectric and ferroelectric properties have been studied. The results of x-ray diffraction reveal that La3+ and Ba2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a pure perovskite structure. After the partial substitution of La3+ for Bi3+ in the (Bi0.94−x Lax Na0.94)0.5Ba0.06TiO3 ceramics (x = 0–0.04), the ceramics exhibit a lower coercive field Ec and a larger remanent polarization Pr. Because of the large Pr and low Ec, the ceramics with x = 0.02–0.04 exhibit optimum piezoelectric properties: d33 = 181–196 pC N−1 and kP = 33.2–36.3%. The depolarization temperature Td decreases with increasing x (x = 0 − 0.04). At the high La3+ level (x = 0.06–0.12), the ceramics exhibit weak ferroelectricity and thus possess very poor piezoelectricity, and the low dielectric anomaly at Td disappears. In addition, the ceramics exhibit a relaxor characteristic, which probably results from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics with x = 0–0.04 may contain both polar and non-polar regions at temperatures above Td, while for the ceramics with x = 0.06–12, the polar and non-polar regions coexist at room temperature.

Synthesis and piezoelectric properties of [Bi1-z(Na1-x-y-zKxLiy)]0.5BazTiO3 lead-free piezoelectric ceramics

[Bi1-z(Na1-x-y-zKxLiy)]0.5BazTiO3 lead-free piezoelectric ceramics were fabricated by ordinary ceramic technique and the piezoelectric and ferroelectric properties of the ceramics were studied. The ceramics can be well sintered at 1,100–1,150 °C for 2 h. X-ray diffraction (XRD) analysis shows that K+, Li+ and Ba2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a solid solution with a single-phase perovskite structure. The introduction of K+, Li+ and Ba2+ into Bi0.5Na0.5TiO3 significantly decreases the coercive field Ec but maintains the large remanent polarization Pr of the materials. The ceramics provide piezoelectric constant d33 of 205 pC/N, electromechanical coupling factor kp of 0.346, remanent polarization Pr of 31.7–38.5 μC/cm2, and coercive field Ec of 3.18–5.16 kV/mm.

THE CHARACTERISTICS OF BiFeO3 MULTIFERROIC THIN FILMS GROWN BY PULSED LASER DEPOSITION

ABSTRACT BiFeO3 (BFO) thin films have been deposited on Pt (111)/TiO2/SiO2/Si substrates by pulsed laser deposition. Various deposition parameters, such as deposition temperature, oxygen pressure in chamber, and deposition time, have been optimized to get good quality BFO thin films. Based on the x-ray diffraction investigation, the single-phase of BFO thin films were successfully deposited at a deposition temperature of 500°C and an oxygen partial pressure of 10 mTorr. The lower oxygen partial pressure leads a lower leakage current from the BFO film capacitors. Even though the BFO film deposited at P(O2) = 10 mTorr and Tdep = 500°C is polycrystalline without preferred orientations, a large remanent polarization Pr of 52 μ C/cm2 at a electric field of 600 kV/cm was observed.

EFFECT OF NIOBIUM DOPING ON PIEZOELECTRIC AND PYROELECTRIC PROPERTIES OF Bi3.5Nd0.5Ti3O12 CERAMICS

ABSTRACT Niobium-doped bismuth titanate (Bi3.5−x/3Nd0.5Ti3−xNbxO12, x = 0 to 0.09) were prepared using a conventional mixed oxide method, and the effects of Nb doping on the dielectric, ferroelectric, piezoelectric and pyroelectric properties of the ceramics were examined. In general, the doping with Nb decreases the relative permittivity ϵ, coercive field Ec and leakage current density J of the ceramics, while increases the remnant polarization Pr, piezoelectric (charge) coefficient d33 and pyroelectric coefficient p. At 6 mol% Nb-doping level, the ceramic exhibit a large Pr (15 μ C/cm2) and a low J (3×10−8 A/cm2) under an electric field of 75 kV/cm, while its d33 and p reach a maximum value of 22 pC/N and 129 μ C/m2 K, respectively. Since the ceramic also has a relatively low ϵ value of 115 (hence a high value of piezoelectric (voltage) coefficient), it is a potential candidate for sensing applications.

The role of inertia in the evolution of spherical dynamos

SUMMARY A numerical parametric study of 3-D spherical dynamos is performed in order to understand the role of inertial effects in the evolution of the simulated dynamo. We vary the Prandtl (Pr) and magnetic Prandtl (Pm) numbers together, maintaining a constant ratio of thermal to magnetic diffusivities and leaving other parameters fixed. For Pr=Pm≥ 1, we find that the solution is only weakly dependent on Pr=Pm, and the principal force balance is between the magnetic, buoyancy and Coriolis forces (MAC balance). At lower values of Pr and Pm, the inertial forces begin to gain importance, and the MAC balance is disturbed. The field becomes less dipolar and weaker, with the effect that a balance between the buoyancy, Coriolis and inertial forces ensues. The low inertia, large Pr=Pm solutions resemble the geomagnetic field more closely, but there are still a few systematic differences between these solutions and the Earth's magnetic field.

Coordination Polymers Based on Inorganic Lanthanide(III) Sulfate Skeletons and an Organic Isonicotinate N-oxide Connector: Segregation into Three Structural Types by the Lanthanide Contraction Effect

Fourteen three-dimensional coordination polymers of general formula [Ln(lNO)(H2O)(SO4)]n, where Ln = La, 1.La; Ce, 2.Ce; Pr, 3.Pr; Nd, 4.Nd; Sm, 5.Sm; Eu, 6.Eu; Gd, 7.Gd; Tb, 8.Tb; Dy, 9.Dy; Ho, 10.Ho; Er. 11.Er; Tm, 12.Tm; Yb, 13.Yb; and Lu, 14.Lu; INO = isonicotinate-N-oxide, have been synthesized by hydrothermal reactions of Ln3+, MnCO3, MnSO4 x H2O, and isonicotinic acid N-oxide (HINO) at 155 degrees C and characterized by single-crystal X-ray diffraction, IR, thermal analysis, luminescence spectroscopy, and the magnetic measurement. The structures are formed by connection of layer, chain, or dimer of Ln-SO4 by the organic connector, INO. They belong to three structural types that are governed exclusively by the size of the ions: type I for the large ions, La, Ce, and Pr; type II for the medium ions, Nd, Sm, Eu, Gd, and Tb; and type III for the small ions, Dy, Ho, Er, Tm, Yb, and Lu. Type I consists of two-dimensional undulate Ln-sulfate layers pillared by INO to form a three-dimensional network. Type II has a 2-fold interpenetration of "3D herringbone" networks, in which the catenation is sustained by extensive pi-pi interactions and O-H...O and C-H...O hydrogen bonds. Type III comprises one-dimensional chains that are connected by INO bridges, resulting in an alpha-Po network. The progressive structural change is due to the metal coordination number decreasing from nine for the large ions via eight to seven for the small ions, demonstrating clearly the effect of lanthanide contraction. The sulfate ion acts as a micro4- or micro3-bridge, connecting two, three, or four metals, and is both mono- and bidentate. The INO ligand acts as a micro3- or micro2-bridge with carboxylate group in syn-syn bridging or bidentate chelating mode. The materials show considerably high thermal stability. The magnetic properties of 4.Nd, 6.Eu, 7.Gd, and 13.Yb and the luminescence properties of 6.Eu and 8.Tb are also investigated.

The onset of buoyancy-driven convecion in a horizontal fluid layer subjected to evaporative cooling

The onset of buoyancy-driven convection in an initially isothermal, quiescent fluid layer experiencing evaporative cooling from above is analyzed under linear theory. Based on propagation theory, the self-similar stability equations are forced. The dimensionless critical time τ c to mark the onset of convective instability is presented as a function of the Rayleigh number Raq and the Prandtl number Pr. The present model predicts that τ c decreases with increasing Pr for a given Raq. When the temporal growth rate of disturbances is considered, the present predictions compare reasonably well with existing experimental data of water. It seems that for large Pr manifest convection is detected at a certain time τ ≅ 4τ c .

Large remanent polarization of 100% polar-axis-oriented epitaxial tetragonal Pb(Zr0.35Ti0.65)O3 thin films

100% polar-axis (c-axis)-oriented epitaxial Pb(Zr0.35Ti0.65)O3 (PZT) thin films were grown and their large remanent polarization (Pr) was directly measured. Perfectly c-axis-oriented epitaxial PZT thin films were obtained on (100)cSrRuO3//(100)SrTiO3 substrates when the deposition temperature increased to 540 °C together with a decrease in the film thickness down to 50 nm. Polarization–electric-field hysteresis loops were well saturated and had a square shape. The Pr of a 50 nm thick film saturated at 0.9 V, and its value was over 90 μC/cm2; almost independent of the measurement frequency within the range from 20 Hz to 1 kHz. This value was in good agreement with the estimated one from the a- and c-axes mixture-oriented epitaxial PZT film having the same composition taking into account the fact that only the c-axis-oriented domain contributed to the polarization. On the other hand, the coercive field value of a perfectly c-axis-oriented film was 140 kV/cm and almost the same as that of the mixture-oriented one having the same film thickness. These results show that PZT has a large Pr applicable for high-density ferroelectric random access memory.

Anomalous Pr Ordering, Pr L3-Edge and Cu K-Edge XANES Studies for the Insulating PrBa2Cu3O7−y System

X-ray absorption near-edge structure (XANES) data for the PrBa2Cu3O7−y (6.21≤7−y≤6.95) insulating system with anomalous Pr antiferromagnetic order are reported. Pr L3-edge XANES indicates that Pr formal valence decreases from 3.17–3.18 for oxygenated samples to 3.09 for oxygen-depleted PrBa2Cu3O6.43, 3.03 for PrBa2Cu3O6.38 and 3. 01 for PrBa2Cu3O6.21. The variation of Pr valence indicates that the doped holes initially stay in the CuO1−y plane and contribute to Cu(I)–Cu(II) transformation in this plane, but gradually move into the CuO2 bi-layers with PrO8 cage and result in the appearance of Pr(IV) localized-hole state with, increasing oxygen content. Cu K-edge XANES indicates that the average Cu formal valence increases from less than 2 in oxygen-depleted region to a value larger than 2 for oxygenated samples. with the estimated Cu valence of 2.24 for PrBa2Cu3O6.95. The small average Cu formal valence or large Pr formal valence is closely related to the absence of superconductivity.

Comparison of crystal structure and electrical properties of tetragonal and rhombohedral Pb(Zr,Ti)O3 films prepared at low temperature by pulsed-metalorganic chemical vapor deposition

The crystal structure and the electrical properties were systematically compared for tetragonal and rhombohedral Pb(Zr,Ti)O3 [PZT] films prepared at various deposition temperatures from 580 °C to 395 °C on (111)Pt/Ti/SiO2/Si substrates by pulsed-metalorganic chemical vapor deposition (pulsed MOCVD). Film orientation changed from (111) to (100) and/or (001) with the decrease in the deposition temperature, but the well-crystallized PZT phase was obtained down to 395 °C. The lattice parameter was almost constant with decreasing deposition temperature, suggesting that the Zr and Ti elements in the films were incorporated into the PZT phase. When the deposition temperature decreased, the leakage current density decreased together with a decrease in surface roughness, especially for tetragonal PZT films. Remanent polarization (Pr) continuously decreased with decreasing deposition temperature down to 395 °C, but was above 20 μC/cm2 even at 395 °C. Specifically, the tetragonal film shows good squareness down to 415 °C. These results show that PZT films with low leakage current density and a large Pr were obtained even at 395 °C by pulsed MOCVD irrespective of the film composition.

Stability of thermocapillary flows in non-cylindrical liquid bridges

The thermocapillary flow in liquid bridges is investigated numerically. In the limit of large mean surface tension the free-surface shape is independent of the flow and temperature fields and depends only on the volume of liquid and the hydrostatic pressure difference. When gravity acts parallel to the axis of the liquid bridge the shape is axisymmetric. A differential heating of the bounding circular disks then causes a steady two-dimensional thermocapillary flow which is calculated by a finite-difference method on body-fitted coordinates. The linear-stability problem for the basic flow is solved using azimuthal normal modes computed with the same discretization method. The dependence of the critical Reynolds number on the volume fraction, gravity level, Prandtl number, and aspect ratio is explained by analysing the energy budgets of the neutral modes. For small Prandtl numbers (Pr = 0.02) the critical Reynolds number exhibits a smooth minimum near volume fractions which approximately correspond to the volume of a cylindrical bridge. When the Prandtl number is large (Pr = 4) the intersection of two neutral curves results in a sharp peak of the critical Reynolds number. Since the instabilities for low and high Prandtl numbers are markedly different, the influence of gravity leads to a distinctly different behaviour. While the hydrostatic shape of the bridge is the most important effect of gravity on the critical point for low-Prandtl-number flows, buoyancy is the dominating factor for the stability of the flow in a gravity field when the Prandtl number is high.

Simulation of a positive column discharge with a one-dimensional radial radiation transport coupled particle-in-cell model

A one-dimensional radial slice of an Ar positive column discharge is simulated with a radiation transport coupled particle-in-cell model. The discharge is maintained by an axial current in the positive column which induces a self-consistent axial electric field. Power balance and radiation efficiency are investigated for variations of axial driving current Iz, gas pressure p, and radius R. The parameter regimes are from 0.1 to 1 cm for radius, 1 mTorr to 20 Torr for gas pressure, from 4 to 14 eV for electron temperature, from 1015 to 1017 m−3 for peak plasma density, and from 0.15 to 50 mA for axial current. The radiation efficiency is related to the product of the pressure and the radius, pR; it is restricted by the large wall loss for small pR and by the collisional quenching of the radiative state for large pR. The optimal value is about pR=1 Torr cm for this parameter regime.

Usefulness of experiments with model fluid for thermocapillary convection—effect of Prandtl number on two-dimensional thermocapillary convection

The floating zone technique is promising to realize large, high-quality crystals under microgravity. Thermocapillary flow, which is the dominant convection in a floating zone under microgravity, has been widely reported in the literature to be extremely sensitive to the Prandtl number Pr. In the present study, the effect of Pr on steady thermocapillary convection is re-evaluated based on both analytical and numerical solutions. The results indicate that an approximate similarity of temperature and velocity structures in a large Pr range is realized under suitable conditions, fixing the Marangoni number Ma, in steady two-dimensional regime.

Instability of a gravity-modulated fluid layer with surface tension variation

Gravity modulation of an unbounded fluid layer with surface tension variations along its free surface is investigated. The stability of such systems is often characterized in terms of the wavenumber, α and the Marangoni number, Ma. In (α, Ma) parameter space, modulation has a destabilizing effect on the unmodulated neutral stability curve for large Prandtl number, Pr, and small modulation frequency, Ω, while a stabilizing effect is observed for small Pr and large Ω. As Ω → ∞ the modulated neutral stability curves approach the unmodulated neutral stability curve. At certain values of Pr and Ω, multiple minima are observed and the neutral stability curves become highly distorted. Closed regions of subharmonic instability are also observed. In (1/Ω, g1Ra)-space, where g1 is the relative modulation amplitude, and Ra is the Rayleigh number, alternating regions of synchronous and subharmonic instability separated by thin stable regions are observed. However, fundamental differences between the stability boundaries occur when comparing the modulated Marangoni–Bénard and Rayleigh–Bénard problems. Modulation amplitudes at which instability tongues occur are strongly influenced by Pr, while the fundamental instability region is weakly affected by Pr. For large modulation frequency and small amplitude, empirical relations are derived to determine modulation effects. A one-term Galerkin approximation was also used to reduce the modulated Marangoni–Bénard problem to a Mathieu equation, allowing qualitative stability behaviour to be deduced from existing tables or charts, such as Strutt diagrams. In addition, this reduces the parameter dependence of the problem from seven transport parameters to three Mathieu parameters, analogous to parameter reductions of previous modulated Rayleigh–Bénard studies. Simple stability criteria, valid for small parameter values (amplitude and damping coefficients), were obtained from the one-term equations using classical method of averaging results.