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Recent advances in microelectromechanical systems often require multifunctional materials, which are designed so as to optimize more than one property. Using density functional theory calculations for alloyed nitride systems, we illustrate how co-alloying a piezoelectric material (AlN) with different nitrides helps tune both its piezoelectric and mechanical properties simultaneously. Wurtzite AlN-YN alloys display increased piezoelectric response with YN concentration, accompanied by mechanical softening along the crystallographic c direction. Both effects increase the electrome-chanical coupling coefficients relevant for transducers and actuators. Resonator applications, however, require superior stiffness, thus leading to the need to decouple the increased piezoelectric response from the softened lattice. We show that co-alloying of AlN with YN and BN results in improved elastic properties while retaining some of the piezoelectric enhancements from YN alloying. This finding may lead to new avenues for tuning the design properties of piezoelectrics through composition-property maps. [ABSTRACT FROM AUTHOR]

A two-stage vapor transport equilibration (VTE) has been employed to mitigate lithium deficiency in single crystals of lithium tantalate, LiTaO3. This work details a low-temperature vapor transport infiltration (VTI) anneal step that establishes a lithium-rich surface layer in the treated samples which annihilates the intrinsic point defect complexes of congruent LiTaO3 while allowing depth and concentration profiles of the point defects to be measured via confocal Raman spectroscopy at different stages in the process. These data are then used to calculate diffusion coefficients for lithium in LiTaO3, which range between 4.2 × 10-11 and 2.9 × 10-10 cm2/s between 950 and 1100 °C. The lithium gradients are removed, and sample chemistry is equilibrated during a second, higher-temperature anneal in an ambient atmosphere and confirmed via additional Raman measurements. Temperature-dependent impedance spectroscopy data are also used to confirm the presence or absence of lithium gradients in these samples and show that lithiation of LiTaO3 takes place at temperatures as low as 950 °C. [ABSTRACT FROM AUTHOR]

The effects of neutron-induced damage on the ferroelectric properties of thin film lead zirconate titanate (PZT) were investigated. Two sets of PbZr0.52Ti0.48O3 films of varying initial quality were irradiated in a research nuclear reactor up to a maximum 1 MeV equivalent neutron fluence of (5.16 ± 0.03) × 1015 cm-2. Changes in domain wall mobility and reversibility were characterized by polarization-electric field measurements, Rayleigh analysis, and analysis of first order reversal curves (FORC). With increasing fluence, extrinsic contributions to the small-signal permittivity diminished. Additionally, redistribution of irreversible hysterons towards higher coercive fields was observed accompanied by the formation of a secondary hysteron peak following exposure to high fluence levels. The changes are attributed to the radiation-induced formation of defect dipoles and other charged defects, which serve as effective domain wall pinning sites. Differences in damage accumulation rates with initial film quality were observed between the film sets suggesting a dominance of pre-irradiation microstructure on changes in macroscopic switching behavior. [ABSTRACT FROM AUTHOR]

The dynamics of oxygen vacancies under external stimuli dominates the performance of many solid‐state devices, including capacitors, oxide memristors, anionic conductors, etc. By means of in situ transmission electron microscopy, it is found in BaTiO3 perovskite nanocrystals that formation of oxygen vacancies due to electrical stressing renders the oxide amorphizable under electron beam illumination, suggesting the presence of a threshold concentration of oxygen vacancy affecting the structural stability of BaTiO3 crystals upon high energy radiation. In contrast to the structural change, the resistivity of the nanocrystal seems not liable to the amorphization prior to dielectric breakdown at higher voltage bias. It is proposed that an increase in oxygen vacancy content promotes oxygen mobility in the perovskite structure allowing electron beam induced electric field to modify the local structure and composition. The in situ observations reveal the central role of oxygen vacancies in the structural stability of perovskites which is of paramount importance to their applications in extreme environments and suggest a potential new route to micro‐processing perovskite oxides using the electron beam via oxygen vacancy management without severely compromising the electric property. [ABSTRACT FROM AUTHOR]

III-nitrides and related alloys are widely used for optoelectronics and as acoustic resonators. Ferroelectric wurtzite nitrides are of particular interest because of their potential for direct integration with Si and wide bandgap semiconductors and unique polarization switching characteristics; such interest has taken off since the first report of ferroelectric Al1−xScxN alloys. However, the coercive fields needed to switch polarization are on the order of MV/cm, which are 1–2 orders of magnitude larger than oxide perovskite ferroelectrics. Atomic-scale point defects are known to impact the dielectric properties, including breakdown fields and leakage currents, as well as ferroelectric switching. However, very little is known about the native defects and impurities in Al1−xScxN and their effect on the dielectric and ferroelectric properties. In this study, we use first-principles calculations to determine the formation energetics of native defects and unintentional oxygen incorporation and their effects on the polarization switching barriers in Al1−xScxN alloys. We find that nitrogen vacancies are the dominant native defects, and unintentional oxygen incorporation on the nitrogen site is present in high concentrations. They introduce multiple mid-gap states that can lead to premature dielectric breakdown and increased temperature-activated leakage currents in ferroelectrics. We also find that nitrogen vacancy and substitutional oxygen reduce the switching barrier in Al1−xScxN at low Sc compositions. The effect is minimal or even negative (increases barrier) at higher Sc compositions. Unintentional defects are generally considered to adversely affect ferroelectric properties, but our findings reveal that controlled introduction of point defects by tuning synthesis conditions can instead benefit polarization switching in ferroelectric Al1−xScxN at certain compositions. [ABSTRACT FROM AUTHOR]

Density-functional theory is used to validate spin-resolved and orbital-resolved metrics of localized electronic states to anticipate ferroic and dielectric properties of BiFeO 3 and BiCrO 3 under epitaxial strain. Using previous investigations of epitaxial phase stability in these systems, trends in properties such as spontaneous polarization and bandgap are compared to trends in atomic orbital occupation derived from projected density of states. Based on first principles theories of ferroic and dielectric properties, such as the Modern Theory of Polarization for spontaneous polarization or Goodenough–Kanamori theory for magnetic interactions, this work validates the sufficiency of metrics of localized electronic states to predict trends in multiple ferroic and dielectric properties. Capabilities of these metrics include the anticipation of the transition from G-Type to C-Type antiferromagnetism in BiFeO 3 under 4.2% compressive epitaxial strain and the interval of C-Type antiferromagnetism from 3% to 7% tensile epitaxial strain in BiCrO 3. The results of this work suggest a capability of localized electronic metrics to predict multiferroic characteristics in the BiX O 3 systems under epitaxial strain, with single or mixed B-site occupation. [ABSTRACT FROM AUTHOR]

Abstract: We have successfully developed transparent polycrystalline Gd2Hf2O7 ceramics with high in‐line transparency. A sol–gel process was used to synthesize the Gd2Hf2O7 powder. Simultaneous thermal gravimetric analysis and differential thermal analysis (TGA/DTA) was used to identify the decomposition sequence as a function of temperature for the as‐synthesized sol–gel powders. The calcined powder is single phase and was formed with an estimated average particle size of 120 nm. Crystallization was confirmed by x‐ray diffraction (XRD) and a single phase was achieved by calcining at 1000°C. The calcined powders were hot‐pressed at 1500°C to achieve >95% theoretical density with closed pore structure followed by a hot isostatic pressing at 1500°C at 207 MPa to achieve a fully dense structure. Microstructural characterization shows a uniform grain size distribution with an average grain size of about 11 μm. In‐line transmission measurements revealed high transparency in the red and infrared. Dielectric properties remain stable with relative permittivity values around 180 and loss tangents less than 0.005 up to 350°C. Thermal conductivity was measured to be ~1.8 W/m°K at room temperature, decreasing to ~1.5 W/m°K by 500°C. [ABSTRACT FROM AUTHOR]

This work uses density-functional theory to model the magnetic properties of bismuth-based perovskite oxides under epitaxial strain. We augment the known transition in BiFeO 3 between rhombohedral-like and tetragonal-like phases occurring at 4.2% compressive epitaxial strain with the variation in magnetic behavior near this boundary. This phase boundary coincides with a transition from G- to C-type magnetic order, as well as with a 90% decrease in the magnitude of the [001]-oriented coupling coefficients. The magnitude of iron magnetization is shown to vary by no more than 3% over the entire range of compressive strain considered. In the BiCrO 3 system, we report a variation in chromium magnetization of over 20%, along with transitions from bulk G-type to regions of C-type order under tensile epitaxial strain and to F-type order under both tensile and compressive epitaxial strains. The region of F-type order stabilized under compression beyond 7.9% epitaxial strain corresponds to a "super-tetragonal" phase structurally similar to the well-known phase of BiFeO 3 exhibiting spontaneous polarization on the order of 150 μ C/cm 2. [ABSTRACT FROM AUTHOR]

Initial crystallization of Pb-deficient, lanthanum modified lead zirconate titanate (PLZT) layers followed by post-crystallization phase conversion can be used to obtain high quality PLZT thin films. However, phase evolution in Pb-deficient PLZT thin films is not well understood. To characterize phase evolution in these films, we developed a new in situ, high-temperature X-ray diffraction (XRD) measurement approach for slow heating rates. The well-characterized Pb-excess PLZT composition was used for comparison and to validate the new XRD setup described herein. During crystallization of Pb-deficient thin films, a Pb-rich/La-poor perovskite phase and Pb-poor/La-rich fluorite phase were observed to form simultaneously. The fluorite phase was observed to partially transform into a secondary perovskite phase at higher temperatures. The results obtained are discussed in view of the current understanding of phase evolution in these materials. The details of the new in situ XRD technique are also presented. [ABSTRACT FROM AUTHOR]

Capacitor technologies are as varied as the applications that they enable, but one of the common themes in advanced capacitors for consumer electronics is a desire for increased capacitance in smaller areas/volumes. The heroic advances of discrete capacitor manufacturers have kept pace with the increasing demands of miniaturization, but a time is quickly approaching when it appears that powder-based fabrication techniques simply will not be able to achieve desired layer thicknesses and capacitance densities. Here, we review the current state of the art and recent advances in the processing science and technology of high-permittivity thin films with a focus on industrially scalable solution-based fabrication processes of perovskite ferroelectric systems that appear to offer the greatest promise for the fabrication of future nanoscale capacitors. [ABSTRACT FROM AUTHOR]

The high permittivity of Pb(Zr,Ti)O3 and (Pb,La)(Zr,Ti)O3—PZT and PLZT, respectively—thin films and the flexibility of chemical solution deposition (CSD) make solution-derived P(L)ZT thin films extremely attractive for integrated capacitor applications. However, Pb-loss or cation segregation during processing results in degraded properties of the final film. Here, we have extended the use of multivariate statistical analysis (MSA) of energy-dispersive spectroscopy (EDS) spectrum images (SIs) in scanning transmission electron microscopy (STEM) to allow the two-dimensional (2D) quantitative analysis of cation segregation and depletion in P(L)ZT thin films. Quantified STEM-EDS SIs allow high-resolution (< ≈10 nm) quantification of these cation distributions. Surface Pb depletion is found after crystallization and is replenished by a unique post-crystallization PbO overcoat+anneal processes. Zr/Ti and La segregation are found to develop in a decidedly nonplanar fashion during crystallization, especially in PLZT 12/70/30 material, highlighting the need for 2D analysis. Quantitative 2D chemical information is essential for improved processing of homogeneous P(L)ZT films with optimal electrical properties. [ABSTRACT FROM AUTHOR]

The high-temperature forms of undoped tantalum pentoxide (H-100Ta2O5) and TiO2–modified Ta2O5 (H-92Ta2O5–8TiO2) were investigated by in situ synchrotron X-ray diffraction and Raman scattering measurements. Two unquenchable and reversible phase transformations were observed in pure H-Ta2O5, while only one was detected for TiO2-stabilized H-Ta2O5. Diffraction studies were consistent with displasive transformations, but hot-stage Raman spectroscopy indicated the existence of transient intermediate forms during the transformations. Use of complementary techniques enabled the reinterpretation of phase transformations in light of a newly proposed crystal structure model for H-Ta2O5, 1 and emphasized the structural contributions of the oxygen sublattice. [ABSTRACT FROM AUTHOR]

A hybrid solution-coated powder method was used to reduce the sintering temperature of TiO2-modified Ta2O5 ceramics. This simple and effective method allowed chemical homogenization and densification to take place below a densification-impeding phase transformation, something that has not been achieved by traditional mixed oxide processing. Combining the coated powder method with a two-stage heat treatment (by which specimens were first densified and then transformed into the high dielectric constant H-Ta2O5 phase) enabled the realization of dense and homogeneous 92Ta2O5–8TiO2 ceramics with dielectric constant values up to 280 at room temperature. [ABSTRACT FROM AUTHOR]

Thin films of Pb(Zr0.4Ti0.6)O3 produced by chemical solution deposition were used to study the effects of stress from different platinized single-crystal substrates on film orientation and resulting electrical properties. Films deposited on MgO preferred a (001) orientation due to compressive stress on the film during cooling through the Curie temperature (TC). Films on Al2O3 were under minimal stress at TC, resulting in a mixture of orientations. Those on Si preferred a (111) orientation due to templating from the bottom electrode. Films oriented in the <001> direction demonstrated lower dielectric constants and higher Pr– and -d31 values than (111) films. [ABSTRACT FROM AUTHOR]

A high-speed and high-power current measurement instrument is described for measuring rapid switching of ferroelectric samples with large spontaneous polarization and coercive field. Instrument capabilities (±200 V, 200 mA, and 200 ns order response) are validated with a LiTaO3 single crystal whose switching kinetics are well known. The new instrument described here enables measurements that are not possible using existing commercial measurement systems, including the observation of ferroelectric switching in large coercive field and large spontaneous polarization Al0.7Sc0.3N thin films. [ABSTRACT FROM AUTHOR]

We present a thermodynamic analysis of the recently discovered nitride ferroelectric materials using the classic Landau–Devonshire approach. Electrostrictive and dielectric stiffness coefficients of Al1−xScxN with a wurtzite structure (6 mm) are determined using a free energy density function assuming a hexagonal parent phase (6/mmm), with the first-order phase transition based on the dielectric stiffness relationships. The results of this analysis show that the strain sensitivity of the energy barrier is one order of magnitude larger than that of the spontaneous polarization in these wurtzite ferroelectrics, yet both are less sensitive to strain compared to classic perovskite ferroelectrics. These analysis results reported here explain experimentally reported sensitivity of the coercive field to elastic strain/stress in Al1−xScxN films and would enable further thermodynamic analysis via phase field simulation and related methods. [ABSTRACT FROM AUTHOR]

Wurtzite ferroelectric materials are promising candidates for energy‐efficient memory technologies, particularly for applications requiring high operating temperatures. Asymmetric wake‐up behaviors, in which the polarization reversal depends both on polarity and cycle number for the first few dozen cycles, must be better understood for reliable device operation. Here, the detailed analysis of the asymmetric wake‐up behavior of thin film Al0.94B0.06N was performed combining time‐resolved switching measurements with Rayleigh analysis, piezoelectric measurements, and etching experiments of progressively switched samples. The analysis shows that the gradual opening of the polarization hysteresis loops associated with wake‐up is driven by a gradual increase in the domain‐wall density and/or domain‐wall mobility with electric field cycle to the polarity opposite to the growth polarity. The insights of this discovery will help to guide interface and polarity design in the eventual deployment of reliable devices based on these materials. [ABSTRACT FROM AUTHOR]

Optical properties of insulators can be dominated by trace-level impurities and/or other defects that may be difficult to identify using direct chemical analysis. The present work investigates the origins of coloration in BaSO 4 powders following exposure to high energy photons (1.33 and 1.17 MeV γ from a 60Co source)using a through the combination ofexperimental and computational predictions of defect energies and a suite of complementary experimental techniques. We conclude that a slight greying observed in some BaSO 4 powders is caused by activation of sulfate radicals that are stabilized by nearby barium vacancies or trace amounts of sodium substitution on the barium site. Electron–hole pairs activated by exposure to gamma irradiation and trapped by these defect couples lead to visible absorption centered around ∼ 650 nm. Such trapped electronic defects are stable at room temperature but can be 'healed' byeither thermal annealing above 300 °Cor ultraviolet bleaching. Such gamma-induced colorationwill therefore have has no impact on the mass density that dominates radiopacity nor on the chemical or physical properties of BaSO 4 and is not an indication of any sort of toxic contamination. [Display omitted] • Gamma-induced darkening in high purity BaSO 4 linked to compensated sulfate radicals. • Calculated energies of defects align well with observed optical absorption around 650 nm. • Extensive characterization and challenge experiments eliminate other impurities as the cause. [ABSTRACT FROM AUTHOR]

The LiTaO3 powders with uniformly sized primary particles have been successfully synthesized using a solid state reaction method. The calcined powders were hot-pressed at 1250°C to form the densest ceramics yet reported of undoped LiTaO3. Neutron and electron backscatter diffraction ( EBSD) analysis confirmed a random distribution of grain orientations in the hot-pressed body. Neutron, X-ray, and EBSD studies all indicated the presence of significant residual stresses in the dense ceramic, likely resulting from the large crystallographic anisotropy in thermal expansion of LiTaO3. In addition, EBSD images revealed several unusual microstructural features, presumably related to exaggerated grain growth. [ABSTRACT FROM AUTHOR]

Oxide materials with the perovskite structure have been used in sensors and actuators for half a century, and halide perovskites transformed photovoltaics research in the past decade. Nitride perovskites have been computationally predicted to be stable, but few have been synthesized, and their properties remain largely unknown. We synthesized and characterized a nitride perovskite lanthanum tungsten nitride (LaWN3) in the form of oxygen-free sputtered thin films, according to spectroscopy, scattering, and microscopy techniques. We report a large piezoelectric response measured with scanning probe microscopy that together with synchrotron diffraction confirm polar symmetry of the perovskite LaWN3. Our LaWN3 synthesis should inspire growth of other predicted nitride perovskites, and measurements of their properties could lead to functional integration with nitride semiconductors for microelectromechanical devices. [ABSTRACT FROM AUTHOR]

High‐Sc Al1–xScxN thin films are of tremendous interest because of their attractive piezoelectric and ferroelectric properties, but overall film quality and reproducibility are widely reported to suffer as x increases. In this study, structural and electrical properties of metastable Al0.6Sc0.4N films are connected with plasma changes during film growth, identified via glow discharge optical emission spectroscopy (GD‐OES), and linked to the target mode changes. This in situ GD‐OES technique uses changes in the N2(I) intensity, correlated with DC bias hysteresis behavior of a Al0.6Sc0.4 target in metallic and poisoned modes, to identify films that subsequently exhibit unacceptable structural and electrical performance. Two representative samples deposited under identical conditions but possessing distinct properties related to phases present in the films are focused on. Films sputtered under a poisoned target mode produce pure wurtzite ferroelectric Al0.6Sc0.4N with a reversible 80 μC cm−1 polarization and 3.1 MV cm−1 coercive field. When identical chamber settings are used but the process starts in metallic mode, a mixed wurtzite/rocksalt film is deposited which exhibits nanometer‐scale changes to the film microstructure and a nonferroelectric response. These results illustrate the utility of optical emission spectroscopy for tracking target mode fluctuations when fabricating metastable materials such as high‐Sc Al1–xScxN films. [ABSTRACT FROM AUTHOR]

Epitaxial ferroelectric wurtzite films exhibiting clear polarization-electric field hysteresis behavior are presented. The coercive field of this epitaxial Al0.7Sc0.3N film on the W/c-sapphire substrate is 0.4 ± 0.3 MV cm−1 (8%) smaller than that of a conventional fiber textured film on a Pt/TiOx/SiO2/Si substrate, attributed to the 0.01 ± 0.007 Å smaller c-axis lattice parameter in the epitaxial film. The strain and decrease in the coercive field most likely originate from epitaxial strain rather than the mismatch in the thermal coefficient of expansion. These results provide insight for further coercive field reduction of wurtzite ferroelectrics using epitaxial mismatch strain. [ABSTRACT FROM AUTHOR]

We apply first-principles density-functional theory (DFT) calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula to predict electrical conductivity in Ta2Ox (0 ≤ x ≤ 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (VOn; n = 0,1+,2+). In the crystalline phase, our DFT calculations suggest that VO0 prefers equatorial O sites, while VO1+ and VO2+ are energetically preferred in the O cap sites of TaO7 polyhedra. Our calculations of DC conductivity at 300 K agree well with experimental measurements taken on Ta2Ox thin films (0.18 ≤ x ≤ 4.72) and bulk Ta2O5 powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta2O5 electronic structure provide further theoretical basis to substantiate VO0 as a donor dopant in Ta2O5. Furthermore, this dopant-like behavior is specific to the neutral case and not observed in either the 1+ or 2+ oxidation states, which suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for VOn in Ta2O5. [ABSTRACT FROM AUTHOR]

We examine the optical activity, birefringence, and transparency of Lanthanum-doped, lead zirconate titanate (PLZT 7/65/35) bulk ceramic wafer sections over visible and near-IR spectra and on heating. Optical transitions are compared to both crystallographic (rhombohedral-cubic) and domain (relaxor-ferroelectric) transitions identified with x-ray diffraction, dielectric, and calorimetry measurements. Optical activity and birefringence are shown to be enhanced for disordered domains near room temperature, to attenuate above the relaxor-ferroelectric transition and to gradually decay above the Curie point regardless of the initial poling state. The results are interpreted in light of the change of crystallographic symmetry due to the local strains induced by ferroelectric architecture. The heterogeneous local strains more strongly influence the optical properties than the macro-scale structure of the polycrystalline PLZT ceramic. This mechanism is significant for understanding optical rotation and birefringence in polycrystalline systems. Finally, the specific rotation (up to 350°/mm) lies among the highest reported for crystalline materials. Along with strong poling contrast and comparatively small dispersion for the unpoled state, these properties are promising for electro-optics applications. [ABSTRACT FROM AUTHOR]

Solution deposition is widely used for the fabrication of lead zirconate titanate (PZT) thin films on platinized silicon substrates. However, phase and texture evolution during the crystallization process is not well understood, particularly due to the difficulty in tracking changes in the thin films in situ during heating. In this work, we characterized phase and texture evolution in situ during heating and crystallization of PZT thin films using high-energy X-ray diffraction. Films were pyrolyzed at either 300 °C or 400 °C and heated at various rates between 0.5 °C/s and ∼150 °C/s. For films that were pyrolyzed at 300 °C, the most rapid heating rates first induced strong intensities from a transient Pt3Pb phase. The Pt3Pb phase inherited the texture of the pre-existing platinum layer. Combined with other observations, the results suggest the conversion of the platinum to the intermetallic phase near the interface due to the interdiffusion of lead. In all experimental variations, the pyrochlore phase was observed to form concurrently with the disappearance of the Pt3Pb phase after which the perovskite phase ultimately crystallized. For films that were pyrolyzed at 400 °C, the Pt3Pb phase was not observed at any of the heating rates; instead, the pyrochlore phase was first observed, followed by the perovskite phase. Independent of the pyrolysis temperature or observation of Pt3Pb, a 111-dominant crystallographic texture formed in the perovskite phase when crystallized using fast heating rates. These results demonstrate that 111 textures in solution-derived PZT thin films are not correlated with the observation of Pt3Pb or other intermetallic or transient phases. [ABSTRACT FROM AUTHOR]

An in situ measurement technique is developed and presented, which utilizes x-rays from a synchrotron source with a two-dimensional detector to measure thin film microstructural and crystallographic evolution during heating. A demonstration experiment is also shown wherein the measured diffraction patterns are used to describe phase and texture evolution during heating and crystallization of solution-derived thin films. The diffraction images are measured sequentially while heating the thin film with an infrared lamp. Data reduction methodologies and representations are also outlined to extract phase and texture information from the diffraction images as a function of time and temperature. These techniques and data reduction methods are demonstrated during crystallization of solution-derived lead zirconate titanate ferroelectric thin films heated at a rate of 30 °C/min and using an acquisition time of 8 s. During heating and crystallization, a PtxPb type phase was not observed. A pyrochlore phase was observed prior to the formation and growth of the perovskite phase. The final crystallized films are observed to have both 111 and 100 texture components. The in situ measurement methodology developed in this work allows for acquiring diffraction images in times as low as 0.25 s and can be used to investigate changes during crystallization at faster heating rates. Moreover, the experiments are shown to provide unique information during materials processing. [ABSTRACT FROM AUTHOR]

Knowledge of accurate values of elastic modulus of (Al1–xScx)N is required for design of piezoelectric resonators and related devices. Thin films of (Al1–xScx)N across the entire composition space are deposited and characterized. Accuracy of modulus measurements is improved and quantified by removing the influence of substrate effects and by direct comparison of experimental results with density functional theory calculations. The 5%–30% Sc compositional range is of particular interest for piezoelectric applications and is covered at higher compositional resolution here than in previous work. The reduced elastic modulus is found to decrease by as much as 40% with increasing Sc concentration in the wurtzite phase according to both experimental and computational techniques, whereas Sc-rich rocksalt-structured films exhibit little variation in modulus with composition. [ABSTRACT FROM AUTHOR]

Abstract: Transparent polycrystalline Gd3TaO7 ceramics were successfully developed. A sol‐gel process was used to synthesize Gd3TaO7 powder with a uniform composition and an estimated average particle size of 100 nm. Simultaneous thermal gravimetric analysis and differential thermal analysis (TGA/DTA) was used to identify the decomposition sequence as a function of temperature for the as‐synthesized sol‐gel powders. Crystallization was confirmed by X‐ray diffraction (XRD) and a single phase was achieved by calcining at 1000°C. The calcined powders were hot‐pressed at 1400°C to achieve >96% theoretical density with closed pore structure followed by a hot isostatic pressing at 1400°C at 207 MPa to achieve a fully dense structure. Microstructural characterization shows a uniform grain size distribution with an average grain size of about 7 μm. In‐line transmission measurements revealed high transparency in the red and infrared. Thermal conductivity was measured to be >1.6 W/mK at room temperature, decreasing to ~1.3 W/mK by 500°C. Dielectric properties remain stable with relative permittivity values just above 200 and loss tangents <0.005 up to 350°C. [ABSTRACT FROM AUTHOR]

As part of a continued push for high permittivity dielectrics suitable for use at elevated operating temperatures and/or large electric fields, modifications of BaTiO3 with Bi( M)O3, where M represents a net-trivalent B-site occupied by one or more species, have received a great deal of recent attention. Materials in this composition family exhibit weakly coupled relaxor behavior that is not only remarkably stable at high temperatures and under large electric fields, but is also quite similar across various identities of M. Moderate levels of Bi content (as much as 50 mol%) appear to be crucial to the stability of the dielectric response. In addition, the presence of significant Bi reduces the processing temperatures required for densification and increases the required oxygen content in processing atmospheres relative to traditional X7R-type BaTiO3-based dielectrics. Although detailed understanding of the structure-processing-property relationships in this class of materials is still in its infancy, this article reviews the current state of understanding of the mechanisms underlying the high and stable values of both relative permittivity and resistivity that are characteristic of BaTiO3-Bi( M)O3 dielectrics as well as the processing challenges and opportunities associated with these materials. [ABSTRACT FROM AUTHOR]

Samples of bulk textured polycrystalline BaTiO3 ceramics were fabricated using a templated grain growth ( TGG) approach in order to investigate effects of polycrystallinity and texture related to ferroelectric domain reversal under high-power drive conditions. Barium titanate platelets were formed via two-step topochemical conversion of bismuth titanate platelets grown via molten salt synthesis, then aligned via tape casting within a matrix of fine BaTiO3 powder. The coarse-grained parts showed a high degree of crystallographic texture after sintering. Combined with ceramics of similar density and polycrystallinity, but random orientation and commercial single-crystal specimens, this sample set enabled direct isolation of crystallographic texture and polycrystallinity as the primary variables for high-power polarization reversal studies. These studies have also demonstrated a link between grain size and polarization reversal time that strongly suggests that grain boundaries serve effectively as nucleation sites during the ferroelectric switching process. [ABSTRACT FROM AUTHOR]

The thermal conductivities of both disordered and self-assembled symmetric polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) copolymer films were measured using time-domain thermoreflectance (TDTR). The variation in out-of-plane thermal conductivity with changing block copolymer thickness is similar to that of PMMA polymer brushes and thick spun-cast films. The results suggest that the intetfaces between the PS and PMMA, and reorganization o f the PS and PMMA chains around these intetfaces, do not significantly affect the thermal transport in these PS-b- PMMA films. However, for thin PS-b-PMMA films, the thermal boundary resistances at the sample interfaces limit the thermal transport. [ABSTRACT FROM AUTHOR]

The thermal conductivity of amorphous TaOx memristive films having variable oxygen content is measured using time domain thermoreflectance. Thermal transport is described by a two-part model where the electrical contribution is quantified via the Wiedemann-Franz relation and the vibrational contribution by the minimum thermal conductivity limit for amorphous solids. The vibrational contribution remains constant near 0.9W/mK regardless of oxygen concentration, while the electrical contribution varies from 0 to 3.3 W/mK. Thus, the dominant thermal carrier in TaOx switches between vibrations and charge carriers and is controllable either by oxygen content during deposition, or dynamically by field-induced charge state migration. [ABSTRACT FROM AUTHOR]

The effects of chemistry, substrate, and processing conditions on through-thickness cation distributions are explored in solution-derived morphotropic composition lead zirconate titanate (PZT) films. Films prepared from chelate-based and conventional sol-gel chemistries were spin cast onto Pt/ZnO/SiO2/Si and Pt/Ti/SiO2/Si substrates and pyrolyzed at 300°C, 350°C, and 400°C prior to crystallization at 700°C either in a preheated furnace or via rapid thermal processing. For films crystallized within a conventional furnace on Pt/ZnO/SiO2/Si substrates no chemical gradients were observed. All films prepared on Pt/Ti/SiO2/Si substrates had increased titanium concentrations near the PZT/Pt interfaces, and the source is shown to be titanium diffusing from the substrate metallization stack. The effect of heating method and rate was explored in films prepared on Pt/ZnO/SiO2/Si substrates with 15°C, 50°C, and 100°C/s heating rates within a rapid thermal annealer. Only one solution chemistry-heating rate combination resulted in the formation of a chemical gradient: a conventional sol-gel chemistry and a 50°C/s heating rate. Infrared spectroscopy of pyrolyzed gel films showed absorption spectra differences in the bonding structure between the two chemistries with the conventional sol-gel-derived films exhibiting a signature more similar to that of a PbTiO3 gel, suggestive of a gel-structure source of gradient formation during crystallization. [ABSTRACT FROM AUTHOR]

Piezoelectric and ferroelectric materials are useful as the active element in non-destructive monitoring devices for high-radiation areas. Here, crystallographic structural refinement (i.e., the Rietveld method) is used to quantify the type and extent of structural changes in PbZr0.5Ti0.5O3 after exposure to a 1 MeV equivalent neutron fluence of 1.7x 1015 neutrons/cm². The results show a measurable decrease in the occupancy of Pb and O due to irradiation, with O vacancies in the tetragonal phase being created preferentially on one of the two O sites. The results demonstrate a method by which the effects of radiation on crystallographic structure may be investigated. [ABSTRACT FROM AUTHOR]

Atom probe tomography ( APT) is a powerful materials characterization technique capable of ppm chemical resolution and near atomic scale spatial resolution. However, owing to a number of factors, the technique has not been widely applied to insulating materials and even less to complex oxides. In this study, we outline the methodology necessary to obtain high-quality results on a technologically relevant complex oxide Pb(Zr,Ti)O3 (or PZT) using laser-assisted APT on both bulk and thin film specimens. We show how, with optimized and well-controlled conditions, APT complements conventional techniques such as STEM- EDS. The correlative information can be used to obtain the nanoscale 3-D chemical information and investigate the nanoscale distribution of cations. Using nearest-neighbor cluster analysis routines, 5-10 nm segregation of B-site cations was detected in bulk sintered PZT 53/47 from chemically prepared powders. No statistically significant segregation of B-site cations was observed in thin film specimens. This work opens new avenues toward understanding the process-structure properties in complex materials at length scales heretofore unachievable. [ABSTRACT FROM AUTHOR]

The crystallization of lead zirconate titanate ( PZT) thin films was evaluated on two different platinum-coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO2 adhesion layer. The Pt deposited on TiO2 exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order ( IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X-ray diffraction at a synchrotron source. The intensity of the Pt3Pb phase indicated that deposition on a highly oriented Pt/TiO2 substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO2 substrate than on the Pt/Ti substrate. [ABSTRACT FROM AUTHOR]

The crystallization behavior of solution-derived lead zirconate titanate ( PZT) thin films in different atmospheric environments was studied using in situ X-ray diffraction. The stability of the transient intermetallic Pt3 Pb phase and perovskite PZT is dependent on oxygen partial pressure during crystallization. Based on the relationship between oxygen partial pressure and the resultant phase stability of intermediate phases, a new route to produce PZT thin films was developed. The new route involves switching atmospheres during crystallization and is shown to mitigate the formation of the transient intermetallic Pt3 Pb phase and to promote the perovskite PZT phase. The route evidences a new and significant variable controlling film synthesis and film microstructure. [ABSTRACT FROM AUTHOR]