Boundary Composition Research Articles

Domain configuration evolution, dielectric, ferroelectric and piezoelectric properties of 0.32PIN–0.345PMN–0.335PT single crystals

Domain configuration evolution with temperature of the unpoled [001]C-oriented 0.32Pb(In1/2Nb1/2)O3–0.345Pb(Mg1/3Nb2/3)O3–0.335PbTiO3 (0.32PIN–0.345PMN–0.335PT) single crystals was studied by the polarized light microscopy (PLM). The optical observation of the domain structures reveals the coexistence of polymorphic ferroelectric phases with mainly ferroelectric monoclinic phase at room temperature and the irreversible domain evolution upon thermal cycling, which induce the high piezoelectric response in such relaxor-based ferroelectric single crystals with the morphotropic phase boundary compositions combined with polarization rotation. The temperature dependent domain evolution and dielectric behavior demonstrate the successive temperature-induced second-order ferroelectric M phase to ferroelectric tetragonal (T) phase (FEM–FET) and first-order ferroelectric T phase to paraelectric cubic (C) phase (FET–PC) ferroelectric phase transitions in the unpoled 0.32PIN–0.345PMN–0.335PT single crystals. Two dielectric loss anomalies were detected around the dielectric anomaly below 100 °C in the poled 0.32PIN–0.345PMN–0.335PT single crystals, indicating that the FEM–FET phase transition can be correlated with two different ferroelectric phase transitions, one is MA–MC, and the other is MC–T phase transition. The FEM–FET phase transition was confirmed further by the energy density measurement. The temperature dependent piezoelectric properties proved that the working temperature of the 0.32PIN–0.345PMN–0.335PT single crystals can reach 130 °C, higher around 50 °C than the Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals, indicating their promising applications in transducers used at elevated temperatures.

Effects of Bi0.5Na0.5HfO3 addition on the phase structure and piezoelectric properties of (K, Na)NbO3‐based ceramics

AbstractLead‐free perovskite (1‐x)(K0.48Na0.48Li0.04)Nb0.95Sb0.05O3‐x(Bi0.5Na0.5)HfO3 piezoelectric ceramics were prepared by a traditional ceramic fabrication method. An investigation was conducted to assess the effects of (Bi0.5Na0.5)HfO3 content on the crystal structure, microstructure, phase‐transition temperatures, and piezoelectric properties of the ceramics. The X‐ray diffraction results, combined with the temperature dependence of dielectric properties, revealed that the ceramics experienced a structural transition from an orthorhombic phase to a tetragonal phase with the addition of (Bi0.5Na0.5)HfO3, and a coexistence of orthorhombic and tetragonal phases was identified in the composition range of 0.005≤x≤0.015. An obviously improved piezoelectric activity was obtained for the ceramics with compositions near the orthorhombic‐tetragonal phase boundary, among which the composition x=0.005 exhibited the maximum values of piezoelectric constant d33, and planar and thickness electromechanical coupling coefficients (kp and kt) of 246 pC/N, 0.435, and 0.554, respectively. Furthermore, the Curie temperature of the ceramics was found decreasing with the increase in (Bi0.5Na0.5)HfO3 content, but still maintaining above 300°C for the phase boundary compositions. These results indicate that the ceramics are promising lead‐free candidate materials for piezoelectric applications.

Structure and Properties of Some Layered U2O5 Phases: A Density Functional Theory Study.

U2O5 is the boundary composition between the fluorite and the layered structures of the UO2→3 system and the least studied oxide in the group. δ-U2O5 is the only layered structure proposed so far experimentally, although evidence of fluorite-based phases has also been reported. Our DFT work explores possible structures of U2O5 stoichiometry by starting from existing M2O5 structures (where M is an actinide or transition metal) and replacing the M ions with uranium ions. For all structures, we predicted structural and electronic properties including bulk moduli and band gaps. The majority of structures were found to be less stable than δ-U2O5. U2O5 in the R-Nb2O5 structure was found to be a competitive structure in terms of stability, whereas U2O5 in the Np2O5 structure was found to be the most stable overall. Indeed, by including the vibrational contribution to the free energy using the frequencies obtained from the optimized unit cells we predict that Np2O5 structured U2O5 is the most thermodynamically stable under ambient conditions. δ-U2O5 only becomes more stable at high temperatures and/or pressures. This suggests that a low-temperature synthesis route should be tested and so potentially opens a new avenue of research for pentavalent uranium oxides.

Boosting Active Contours for Weld Pool Visual Tracking in Automatic Arc Welding

Detecting the shape of the non-rigid molten metal during welding, so-called weld pool visual sensing, is one of the central tasks for automating arc welding processes. It is challenging due to the strong interference of the high-intensity arc light and spatters as well as the lack of robust approaches to detect and represent the shape of the nonrigid weld pool. We propose a solution using active contours including an prior for the weld pool boundary composition. Also, we apply Adaboost to select a small set of features that captures the relevant information. The proposed method is applied to weld pool tracking and the presented results verified its feasibility.

Phase transition, switching characteristics of MPB compositions and large strain in lead-free (Bi 0.5 Na 0.5 )TiO 3 -based piezoceramics

Abstract In this study, the switching characteristics of MPB compositions of (1-x-y)(Bi0.5Na0.5)TiO3-xKNbO3-ySrTiO3 (abbreviated as BNT-KN-ST) and temperature- and composition-driven strain behavior, dielectric, ferroelectric (FE), piezoelectric, and pyroelectric properties were systematically explored to achieve lead-free piezoelectric materials with large strain response for practical applications of piezoelectric actuators. The piezoelectric coefficient (d33) declined dramatically and normalized strain Smax/Emax increased markedly as the morphotropic phase boundary (MPB) compositions shifted away from the MPB (I) into the MPB (II) where the ferroelectric rhombohedral and relaxor pseudo-cubic phases coexisted at around critical composition. The critical compositions for the indicated system exhibited enhanced strain response, and at room temperature a high strain of 0.34% with normalized strain Smax/Emax = 486 p.m./V was gained for the critical composition 0.90BNT-0.05KN-0.05ST. The source of the achieved large strain was sought based on the X-ray diffraction (XRD) and Raman-spectra structure analysis, macroscopic properties, thermal depolarization progress, and temperature-dependent correlations of both polarization and strain, and the results indicated that it derived from the phase transformation contribution from ergodic relaxor (ER) to FE phases. Moreover, the present work also established the relationship between the MPB composition and tolerance factor t in BNT-based ceramics, and demonstrated that the t corresponding to the formation of MPB located in a quite narrow range. As a result, we believe that this study will open the door to quickly detect the approximate MPB region for BNT-based solid solutions.

Guest enclathration and structural transition in CO2 + N2 + methylcyclopentane hydrates and their significance for CO2 capture and sequestration

The phase equilibria, structural transition, gas uptake, and composition of CO2+N2+methylcyclopentane (MCP) hydrates were investigated for their potential applications in CO2 capture and sequestration. Thermodynamic stability conditions indicated that flue gas could form sH hydrates in the presence of MCP at a reduced pressure and an elevated temperature. Powder X-ray diffraction (PXRD) and Raman analyses revealed that the structural transition of CO2+N2+MCP hydrates occurs from sH to sI with increasing CO2 concentration and that both sH and sI coexist at a boundary composition of CO2 (20%)+N2 (80%). In situ Raman spectroscopy provided direct evidence of the enclathration of CO2 and MCP in cages of sH hydrates under highly N2-rich conditions. The sH CO2+N2+MCP hydrates demonstrated slightly lower gas uptakes and CO2 selectivity in the hydrate phase than corresponding sI CO2+N2 hydrates, despite their thermodynamic advantages. The overall experimental results obtained in this study can help create a better understanding of guest enclathration and structural transition in sH hydrates and thus provide new insights into sH hydrate-based CO2 capture and sequestration using flue gas.

Investigation of morphotropic phase boundaries in PIN–PSN–PT relaxor ferroelectric ternary systems with high Tr-t and Tc phase transition temperatures

New morphotropic phase boundary (MPB) compositions with relatively high Tcs were projected in Pb(In1/2Nb1/2)O3–Pb(Sc1/2Nb1/2)O3–PbTiO3 (PIN–PSN–PT) solid solution based on the perovskite tolerance factor, and were experimentally confirmed. The phase structure, dielectric, pyroelectric, piezoelectric and ferroelectric properties of PIN–PSN–PT ceramics were investigated. The rhombohedral–tetragonal phase transition temperatures Tr-t on the order of 189–210°C, Curie temperatures Tc on the order of 274–285°C and piezoelectric coefficients d33 in the range of 310–360pC/N, were achieved in xPIN– (1−x)PSN–0.37PT (x=0.15–0.23) ceramics, demonstrating a promising relaxor–PbTiO3 system with high phase transition temperatures. In addition, the maps of Tc, Tr-t, d33 and εr with respect to composition were established, based on which, a clear direction for composition screening in future crystal growth of the PIN–PSN–PT system was given.

Temperature and electric field-induced phase transitions in (1 − x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

Field-induced phase transitions in [111]- and [110]-oriented relaxor ferroelectric (1 − x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystals in the morphotropic phase boundary (MPB) composition range were examined through temperature-dependent complex capacitance measurements. Two first-order phase transitions from paraelectric cubic to ferroelectric tetragonal and then to ferroelectric rhombohedral phases were observed in the unpoled crystal. Additional weak dielectric anomalies were observed at a temperature of ~ 40 °C (in both crystals) and ~ 90 °C (in [110] crystals) in the poled samples. These weak anomalies disappeared when cooling the crystal from higher temperature but within the ferroelectric tetragonal phase. The new anomalies were attributed to the formation of field-induced metastable phases, which were unstable with temperature modulation.

Effects on structure and properties of BCZT lead-free piezoelectric ceramics by rare-earth doping

ABSTRACT1 mol% rare-earth element doped [(Ba0.85Ca0.15)0.99Re0.01](Zr0.1Ti0.9)O3 (BCZT-Re, Re = La, Sm, Yb, Eu and Er) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing using high-purity carbonates and oxides as raw materials. The BCZT-Re ceramics sintered at 1450°C exhibit pure rhombohedral perovskite structure approaching the morphotropic phase boundary (MPB) composition accompanied by different relative density and grain size distribution. The dielectric behavior of the BCZT-Re ceramics approaches normal ferroelectrics but with slightly broad dielectric response peaks, and can be fitted well by the Curie-Weiss law above the Curie temperature TC but in a limited temperature range. Besides the La doping, the other BCZT-Re ceramics present symmetric and saturated P-E hysteresis loops, in which the BCZT-Eu ceramics exhibit apparently large values of polarization remnant Pr and coercive field Ec. The Pr and Ec values decrease rapidly around 80–90°C, depending on compositions, in the BCZT-Re ceramics, determining their safe use temperatures. Excellent fluorescence performance with different photoluminescence emission intensity and light color is induced by the rare-earth doping in the BCZT-Re ceramics, which can meet the requirements of the multifunctional applications using the ferroelectric-based materials.

A Combined TEM/STEM and Micromagnetic Study of the Anisotropic Nature of Grain Boundaries and Coercivity in Nd-Fe-B Magnets

The nanoanalytical high resolution TEM/STEM investigation of the intergranular grain boundary phase of anisotropic sintered and rapidly quenched heavy rare earth-free Nd-Fe-B magnet materials revealed a difference in composition for grain boundaries parallel (large Fe-content) and perpendicular (low Fe content) to the alignment direction. This behaviour vanishes in magnets with a high degree of misorientation. The numerical finite element micromagnetic simulations are based on the anisotropic compositional behaviour of GBs and show a decrease of the coercive field with an increasing thickness of the grain boundary layer. The magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries parallel to thec-axis and secondly as Néel domain wall perpendicular to thec-axis into the adjacent hard magnetic grains. The increasing misalignment of grains leads to the loss of the anisotropic compositional behaviour and therefore to an averaged value of the grain boundary composition. In this case the simulations show an increase of the coercive field compared to the anisotropic magnet. The calculated coercive field values of the investigated magnet samples are in the order ofμ0HcJ=1.8 T–2.1 Tfor a mean grain boundary thickness of 4 nm, which agrees perfectly with the experimental data.

Enhanced ionic conductivity in electroceramics by nanoscale enrichment of grain boundaries with high solute concentration.

The enhancement of oxygen ionic conductivity by over two orders of magnitude in an electroceramic oxide is explicitly shown to result from nanoscale enrichment of a grain boundary layer or complexion with high solute concentration. A series of CaxCe1-xO2-δ polycrystalline oxides with fluorite structure and varying nominal Ca2+ solute concentration elucidates how local grain boundary composition, rather than structural grain boundary character, primarily regulates ionic conductivity. A correlation between high grain boundary solute concentration above ∼40 mol%, and four orders of magnitude increase in grain boundary conductivity is explicitly shown. A correlated experimental approach provides unique insights into fundamental grain boundary science, and highlights how novel aspects of nanoscale grain boundary design may be employed to control ion transport properties in electroceramics.

The effect of the local chemical composition of grain boundaries on the corrosion resistance of a titanium alloy

The influence of the structural-phase state of grain boundaries in a Ti4Al2V (commercial PT3V grade) pseudo-alpha-titanium alloy on its susceptibility to hot-salt intergranular corrosion (IGC) has been studied. It is established that IGC-tested alloy samples exhibit corrosion-induced defects of two types. More extended defects of the first type occur at the V-rich boundaries of coarse grains, while short defects of the second type reside at the grain boundaries with composition close to that of the grain body. The existence of the two types of IGC defects is explained by the classical theory of galvanic microcouples (microcells), according to which the IGC intensity is proportional to the difference of corrosion-active impurity concentrations between the grain boundary and body.

Micromagnetic simulation of the influence of grain boundary on cerium substituted Nd-Fe-B magnets

A three-dimensional finite element model was performed to study the magnetization reversal of (CexNd1-x)2Fe14B nanocomposite permanent magnets. The influences of volume fraction, width and performance parameters of the grain boundary (GB) composition on the coercivity were analyzed by the method of micromagnetic simulation. The calculation results indicate that the structure and chemistry of GB phase play important roles in Nd2Fe14B-based magnets. An abnormal increase in the value of coercivity is found to be connected with the GB phase, approximately when the percentage of doped cerium is between 20% and 30%. While the coercivity decreases directly with the increase in cerium content instead of being abnormal when there is no GB phase in magnets at all or the value of magnetocrystalline anisotropy or exchange integral is too large.

Coupled domain wall motion, lattice strain and phase transformation in morphotropic phase boundary composition of PbTiO3-BiScO3 piezoelectric ceramic

High energy synchrotron X-ray diffraction, in situ with electric field, was carried out on the morphotropic phase boundary composition of the piezoelectric alloy PbTiO3-BiScO3. We demonstrate a strong correlation between ferroelectric-ferroelastic domain reorientation, lattice strain and phase transformation. We also show the occurrence of the three phenomena and persistence of their correlation in the weak field regime.

Aerosol measurements during COPE: composition, size, and sources of CCN and INPs at the interface between marine and terrestrial influences

Abstract. Heavy rainfall from convective clouds can lead to devastating flash flooding, and observations of aerosols and clouds are required to improve cloud parameterisations used in precipitation forecasts. We present measurements of boundary layer aerosol concentration, size, and composition from a series of research flights performed over the southwest peninsula of the UK during the COnvective Precipitation Experiment (COPE) of summer 2013. We place emphasis on periods of southwesterly winds, which locally are most conducive to convective cloud formation, when marine air from the Atlantic reached the peninsula. Accumulation-mode aerosol mass loadings were typically 2–3 µg m−3 (corrected to standard cubic metres at 1013.25 hPa and 273.15 K), the majority of which was sulfuric acid over the sea, or ammonium sulfate inland, as terrestrial ammonia sources neutralised the aerosol. The cloud condensation nuclei (CCN) concentrations in these conditions were ∼ 150–280 cm−3 at 0.1 % and 400–500 cm−3 at 0.9 % supersaturation (SST), which are in good agreement with previous Atlantic measurements, and the cloud drop concentrations at cloud base ranged from 100 to 500 cm−3. The concentration of CCN at 0.1 % SST was well correlated with non-sea-salt sulfate, meaning marine sulfate formation was likely the main source of CCN. Marine organic aerosol (OA) had a similar mass spectrum to previous measurements of sea spray OA and was poorly correlated with CCN. In one case study that was significantly different to the rest, polluted anthropogenic emissions from the southern and central UK advected to the peninsula, with significant enhancements of OA, ammonium nitrate and sulfate, and black carbon. The CCN concentrations here were around 6 times higher than in the clean cases, and the cloud drop number concentrations were 3–4 times higher. Sources of ice-nucleating particles (INPs) were assessed by comparing different parameterisations used to predict INP concentrations, using measured aerosol concentrations as input. The parameterisations based on total aerosol produced INP concentrations that agreed within an order of magnitude with measured first ice concentrations at cloud temperatures as low as −12 °C. Composition-specific parameterisations for mineral dust, fluorescent particles, and sea spray OA were 3–4 orders of magnitude lower than the measured first ice concentrations, meaning a source of INPs was present that was not characterised by our measurements and/or one or more of the composition-specific parameterisations greatly underestimated INPs in this environment.

Probing the boundaries of ceramics

Ceramics Ceramics are important but underappreciated materials for numerous technologies. Diercks et al. investigate the connection between electrical properties and local chemistry in neodymium-doped ceria. They show that macroscopic changes in properties such as electrical conductivity are tied to the chemical composition of the grain boundaries, which make up a tiny fraction of the overall volume. High-precision maps provide a method for understanding the relationship between microscopic and macroscopic properties, which can be exploited for optimizing materials design. J. Mater. Chem. A 10.1039/c5ta10064j (2016).

Irreversible phase transition characteristic of 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 single crystals by domain observation

In situ temperature dependent ferroelectric domains dynamic evolution of the (001)pc oriented 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 (PZNT91/9) single crystals was observed by polarized light microscopy (PLM) and real time synchrotron-radiation (SR) X-ray white-beam topography. Intricate domain structures including monoclinic phase are distinguished by PLM at room temperature, and irreversible domain configuration dynamic evolution upon thermal cycling is observed by both methods. Such irreversible domain evolution combined with coexistence of multi-phases and polarization rotation may be related to the extraordinary piezoelectric performance in the ferroelectric single crystals with the morphotropic phase boundary (MPB) compositions.

Piezoelectric and dielectric properties of 0.995K0.48Na0.48Li0.04Nb(1−x)SbxO3–0.005BiAlO3 lead-free piezoelectric ceramics

Lead-free 0.995K0.48Na0.48Li0.04Nb(1−x)SbxO3–0.005BiAlO3 piezoelectric ceramics with perovskite structure were designed and prepared with conventional ceramic fabrication techniques. The phase transitions of the ceramics were determined by X-ray diffraction patterns and the temperature dependence of dielectric properties. The ceramics possessed an orthorhombic–tetragonal phase boundary with x=0 and exhibited the coexistence of rhombohedral–orthorhombic and orthorhombic–tetragonal phase boundaries at around room temperature, with 0.02≤x≤0.03. Upon further increasing the Sb content, the crystal structure transformed to the rhombohedral-tetragonal phase coexistence in the composition range of 0.04≤x≤0.05. Next, the phase structure turned to a sole rhombohedral symmetry with x≥0.06. A clearly enhanced piezoelectric activity was demonstrated for the ceramic with the rhombohedral-tetragonal phase boundary composition x=0.05, where the values of piezoelectric constant d33, planar and thickness electromechanical coupling coefficients reached 205 pC/N, 0.360 and 0.437, respectively.

Dielectric and piezoelectric properties of high curie temperature 0.63Bi(Mg1/2Ti1/2)O3–0.37PbTiO3 single crystals with morphotropic phase boundary composition

Abstract Novel perovskite ferroelectric 0.63Bi(Mg 1/2 Ti 1/2 )O 3 –0.37PbTiO 3 (0.63BMT–0.37PT) single crystals with a composition around the morphotropic phase boundary (MPB) were successfully grown by a self-flux method. They presented Curie temperature ( T c ) about 460 °C and a rhombohedral to tetragonal phase transition temperature (Tr-t) 249 °C. The piezoelectric constant d 33 for (001) oriented 0.63BMT–0.37PT single crystals reached 320pC/N, which was higher than that (208pC/N) in the tetragonal phase 0.38BMT–0.62PT crystals. The large piezoelectric constant d 33 and high T c make BMT–PT single crystals promising candidates used for the next generation of high performance and high temperature actuators and transducers.

Relation between structure and piezoelectric properties of (1-x-y)PbZrO3-xPbTiO3-yPb(Ni1/3Nb2/3)O3 ceramics near triple point composition

The structural and piezoelectric properties of (1-x-y)PbZrO3-xPbTiO3-yPb(Ni1/3Nb2/3)O3 [(1-x-y)PZ-xPT-yPNN] ceramics near the triple point were investigated. The 0.16PZ-0.34PT-0.5PNN ceramic with a triple point composition exhibited a large d33, kp and ε33T/εo values of 855 pC/N, 0.68 and 5800, respectively. However, its g33 and d33 x g33 values were relatively small because of its large ε33T/εo. Similar results were obtained for specimens with rhombohedral-tetragonal or pseudocubic-tetragonal morphotropic phase boundary (MPB) compositions. However, specimens with a rhombohedral structure near the rhombohedral-tetragonal MPB exhibited large g33 and d33 x g33 values because of their large d33 and small ε33T/εo that can be explained by their polarization characteristics. In particular, 0.23PZ-0.36PT-0.41PNN ceramic exhibited large g33 and d33 x g33 values of 30.2×10−3 Vm/N and 22.6×10−12m2/N, respectively, thus making it a good candidate for piezoelectric energy harvesters and multilayer actuators.