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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

A Hubble space telescope search for a sub-Earth-sized exoplanet in the GJ 436 system

The detection of small planets orbiting nearby stars is an important step toward the identification of Earth twins. In previous work using the Spitzer Space Telescope, we found evidence to support at least one sub-Earth-sized exoplanet orbiting the nearby mid-M dwarf star GJ 436. As a follow up, here we used the Hubble Space Telescope (HST) to investigate the existence of one of these candidate planets, UCF-1.01, by searching for two transit signals as it passed in front of its host star. Interpretation of the data hinges critically on correctly modeling and removing the Wide Field Camera 3 (WFC3) instrument systematics from the light curves. Building on previous HST work, we demonstrate that WFC3 analyses need to explore the use of a quadratic function to fit a visit-long time-dependent systematic. This is important for establishing absolute transit and eclipse depths in the white light curves of all transiting systems. The work presented here exemplifies this point by putatively detecting the primary transit of UCF-1.01 with the use of a linear trend. However, using a quadratic trend, we achieve a better fit to the white light curves and a reduced transit depth that is inconsistent with previous Spitzer measurements. Furthermore, quadratic trends with or without a transit model component produce comparable fits to the available data. Using extant WFC3 transit light curves for GJ 436b, we further validate the quadratic model component by achieving photon-limited model fit residuals and consistent transit depths over multiple epochs. We conclude that, when we fit for a quadratic trend, our new data contradict the prediction of a sub-Earth-sized planet orbiting GJ 436 with the size, period, and ephemeris posited from the Spitzer data by a margin of 3.1σ.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Conglomeration of kilometer-sized planetesimals

We study the efficiency of forming large bodies, starting from a sea of equal-sized planetesimals. This is likely one of the earlier steps of planet formation and relevant for the formation of the asteroid belt, the Kuiper Belt, and extrasolar debris disks. Here we consider the case that the seed planetesimals do not collide frequently enough for collisions to be dynamically important (the collisionless limit), using a newly constructed conglomeration code, and by carefully comparing numerical results with analytical scalings. In the absence of collisional cooling, as large bodies grow by accreting small bodies, the velocity dispersion of the small bodies (u) is increasingly excited. Growth passes from the well-known runaway stage (when u is higher than the big bodies’ hill velocity) to the newly discovered trans-hill stage (when u and big bodies both grow, but u remains at the big bodies’ hill velocity). We find, concurring with the analytical understandings developed by Lithwick, as well as previous numerical studies, that a size spectrum dn/dR∝R{sup −4} results, and that the formation efficiency, defined as the mass fraction in bodies much larger than the initial size, is ∼ a few×R{sub ⊙}/a, or ∼10{sup −3} at the distance of the Kuiper Belt. We argue that this extreme inefficiency invalidates the conventional conglomeration model for the formation of both our Kuiper Belt and extrasolar debris disks. New theories, possibly involving direct gravitational collapse, or strong collisional cooling of small planetesimals, are required.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Orbital survival of meter-size and larger bodies during gravitationally unstable phases of protoplanetary disk evolution

A long-standing problem in the collisional accretion of terrestrial planets is the possible loss of m-size bodies through their inward migration onto the protostar as a result of gas drag forces. Such inward migration can be halted, and indeed even reversed, in a protoplanetary disk with local pressure maxima, such as marginally gravitationally unstable (MGU) phases of evolution, e.g., FU Orionis events. Results are presented for a suite of three-dimensional models of MGU disks extending from 1 to 10 AU and containing solid particles with sizes of 1 cm, 10 cm, 1 m, or 10 m, subject to disk gas drag and gravitational forces. These hydrodynamical models show that over disk evolution time scales of ∼6×10{sup 3} years or longer, during which over half the gaseous disk mass is accreted by the protostar, very few 1 and 10 m bodies are lost through inward migration: most bodies survive and orbit stably in the outer disk. A greater fraction of 1 and 10 cm particles are lost to the central protostar during these time periods, as such particles are more closely tied to the disk gas accreting onto the protostar, but even in these cases, a significant fraction survive and undergo transport from the hot inner disk to the cold outer disk, perhaps explaining the presence of small refractory particles in Comet Wild 2. Evidently MGU disk phases offer a means to overcome the m-sized migration barrier to collisional accumulation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

HELIUM ATMOSPHERES ON WARM NEPTUNE- AND SUB-NEPTUNE-SIZED EXOPLANETS AND APPLICATIONS TO GJ 436b

Warm Neptune- and sub-Neptune-sized exoplanets in orbits smaller than Mercury’s are thought to have experienced extensive atmospheric evolution. Here we propose that a potential outcome of this atmospheric evolution is the formation of helium-dominated atmospheres. The hydrodynamic escape rates of Neptune- and sub-Neptune-sized exoplanets are comparable to the diffusion-limited escape rate of hydrogen, and therefore the escape is heavily affected by diffusive separation between hydrogen and helium. A helium atmosphere can thus be formed—from a primordial hydrogen–helium atmosphere—via atmospheric hydrodynamic escape from the planet. The helium atmosphere has very different abundances of major carbon and oxygen species from those of a hydrogen atmosphere, leading to distinctive transmission and thermal emission spectral features. In particular, the hypothesis of a helium-dominated atmosphere can explain the thermal emission spectrum of GJ 436b, a warm Neptune-sized exoplanet, while also being consistent with the transmission spectrum. This model atmosphere contains trace amounts of hydrogen, carbon, and oxygen, with the predominance of CO over CH{sub 4} as the main form of carbon. With our atmospheric evolution model, we find that if the mass of the initial atmosphere envelope is 10{sup −3} planetary mass, hydrodynamic escape can reduce the hydrogen abundance in the atmosphere by several orders of magnitude in ∼10 billion years. Observations of exoplanet transits may thus detect signatures of helium atmospheres and probe the evolutionary history of small exoplanets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The sizes of candidate galaxies z∼ 9−10: Confirmation of the bright candels sample and relation with luminosity and mass

Recently, a small sample of six z ∼ 9–10 candidates was discovered in CANDELS that are ∼10−20× more luminous than any of the previous z ∼ 9–10 galaxies identified over the HUDF/XDF and CLASH fields. We measure the sizes of these candidates to map out the size evolution of galaxies from the earliest observable times. Their sizes are also used to provide a valuable constraint on whether these unusual galaxy candidates are at high redshift.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

On the size and mass of photoionized clouds in extended spiral galaxy halos

The size and mass of two circumgalactic medium (CGM) clouds in the halo (impact parameter = 65 kpc) of a nearby late-type galaxy, MGC-01-04-005 (cz=1865 km s{sup −1}), are investigated using a close triplet of QSO sight lines (the “LBQS Triplet”). Far ultraviolet spectra obtained with the Cosmic Origins Spectrograph on board the Hubble Space Telescope find two velocity components in Lyα at ∼1830 and 1900 km s{sup −1} in two of these sight lines, requiring minimum transverse cloud sizes of ⩾10 kpc. A plausible, but not conclusive, detection of C iv 1548 Å absorption at the higher velocity in the third sight line suggests an even larger lower limit of ⩾23 kpc for that cloud. Using various combinations of constraints, including photoionization modeling for one absorber, lower limits on masses of these two clouds of ≳10{sup 6}M{sub ⊙} are obtained. Ground-based imaging and long-slit spectroscopy of MCG-01-04-005 obtained at the Apache Point Observatory 3.5 m telescope find it to be a relatively normal late-type galaxy with a current star formation rate (SFR) of ∼0.01M{sub ⊙} yr{sup −1}. GALEX photometry finds an SFR only a few times higher over the last 10{sup 8} years. We conclude that the CGM clouds probed by these spectra are typical because they are at impact parameters of 0.4–0.5 R{sub vir} from a rather typical, non-starbursting late-type galaxy; thus, these size and mass results should be generic for this class. Therefore, at least some CGM clouds are exceptionally large and massive.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Morphologies of ∼190,000 galaxies at z = 0–10 revealed with HST legacy data. I. size evolution

We present the redshift evolution of the galaxy effective radius r{sub e} obtained from the Hubble Space Telescope (HST) samples of ∼190,000 galaxies at z = 0–10. Our HST samples consist of 176,152 photo-z galaxies at z = 0–6 from the 3D-HST+CANDELS catalog and 10,454 Lyman break galaxies (LBGs) at z = 4–10 identified in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), HUDF 09/12, and HFF parallel fields, providing the largest data set to date for galaxy size evolution studies. We derive r{sub e} with the same technique over the wide redshift range of z = 0–10, evaluating the optical-to-UV morphological K correction and the selection bias of photo-z galaxies+LBGs as well as the cosmological surface-brightness dimming effect. We find that r{sub e} values at a given luminosity significantly decrease toward high z, regardless of statistics choices (e.g., r{sub e}∝(1+z){sup −1.10±0.06} for median). For star-forming galaxies, there is no evolution of the power-law slope of the size–luminosity relation and the median Sérsic index (n∼1.5). Moreover, the r{sub e} distribution is well represented by log-normal functions whose standard deviation σ{sub lnr{sub e}} does not show significant evolution within the range of σ{sub lnr{sub e}}∼0.45−0.75. We calculate the stellar-to-halo size ratio from our r{sub e} measurements and the dark-matter halo masses estimated from the abundance-matching study, and we obtain a nearly constant value of r{sub e}/r{sub vir}=1.0%−3.5% at z = 0–8. The combination of the r{sub e}-distribution shape+standard deviation, the constant r{sub e}/r{sub vir}, and n∼1.5 suggests a picture in which typical high-z star-forming galaxies have disk-like stellar components in a sense of dynamics and morphology over cosmic time of z∼0−6. If high-z star-forming galaxies are truly dominated by disks, the r{sub e}/r{sub vir} value and the disk-formation model indicate that the specific angular momentum of the disk normalized by the host halo is j{sub d}/m{sub d}≃0.5−1. These are statistical results for major stellar components of galaxies, and the detailed study of clumpy subcomponents is presented in the paper II.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

On the visible size and geometry of aggressively expanding civilizations at cosmological distances

If a subset of advanced civilizations in the universe choose to rapidly expand into unoccupied space, these civilizations would have the opportunity to grow to a cosmological scale over the course of billions of years. If such life also makes observable changes to the galaxies they inhabit, then it is possible that vast domains of life-saturated galaxies could be visible from the Earth. Here, we describe the shape and angular size of these domains as viewed from the Earth, and calculate median visible sizes for a variety of scenarios. We also calculate the total fraction of the sky that should be covered by at least one domain. In each of the 27 scenarios we examine, the median angular size of the nearest domain is within an order of magnitude of a percent of the whole celestial sphere. Observing such a domain would likely require an analysis of galaxies on the order of a Gly from the Earth.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Controlling the size of non-axisymmetric magnetic footprints using resonant magnetic perturbations

The structure of the non-axisymmetric heat load distribution at the divertor plates is determined not only by the toroidal but also from the poloidal spectrum of non-axisymmetric field perturbations. Whether they are intrinsic, like error fields, or they are applied through 3D coils, the non-axisymmetric fields produce complex 3D edge magnetic topologies (footprints) that alter the properties of the heat and particle flux distributions on the divertor target plates. In this manuscript, a study of the impact of applied 3D field poloidal spectrum on the footprint size and structure is done for the DIII-D tokamak using the resistive MHD code M3D-C1 coupled with the field line tracing code TRIP3D. To resolve the impact of the poloidal spectrum of the magnetic perturbation, the relative phase of the two rows of in-vessel 3D coils used to produce both a n = 2 and a n = 3 perturbation is varied, where n is the toroidal harmonic of the magnetic perturbation. This shows that the largest footprint is predicted when the relative phase of the two rows is close to zero, which is also where the resonant coupling with the plasma is maximized. These results suggest that it will be challenging to decouple the footprint size from the requisite resonant coupling for RMP–ELM control. The correlation between the measured heat load and particle flux distributions at the outer divertor plates in DIII-D and the magnetic measurements is in good agreement with the predicted dependence of the magnetic footprint size on the amplitude of the resonant component of the plasma response.

3D fields↗
DOE OSTI2013

THE SIZE-VIRIAL RADIUS RELATION OF GALAXIES

I use the abundance matching ansatz, which has proven to be successful in reproducing galaxy clustering and other statistics, to derive estimates of the virial radius, R{sub 200}, for galaxies of different morphological types and a wide range of stellar masses. I show that over eight orders of magnitude in stellar mass galaxies of all morphological types follow an approximately linear relation between half-mass radius of their stellar distribution, r{sub 1/2}, and virial radius, r{sub 1/2} Almost-Equal-To 0.015 R{sub 200}, with scatter of Almost-Equal-To 0.2 dex. Such scaling is in remarkable agreement with the expectation of models that assume that galaxy sizes are controlled by halo angular momentum, r{sub 1/2}{proportional_to}{lambda}R{sub 200}, where {lambda} is the spin of galaxy parent halo. The scatter about the relation is comparable with the scatter expected from the distribution of {lambda}. Moreover, I show that when the stellar and gas surface density profiles of galaxies of different morphological types are rescaled by the radius r{sub n} = 0.015 R{sub 200}, the rescaled profiles follow approximately universal exponential (for late types) and de Vaucouleurs (for early types) form with scatter of only Almost-Equal-To 30%-50% at R Almost-Equal-To 1-3r{sub n} . Remarkably, both late- and early-type galaxies have similar mean stellar surface density profiles at R {approx}> 1r{sub n} . The main difference between their stellar distributions is thus at R < r{sub n} . The results of this study imply that galaxy sizes and radial distribution of baryons are shaped primarily by properties of their parent halos and that the sizes of both late-type disks and early-type spheroids are controlled by halo angular momentum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

IN SITU MEASUREMENTS OF THE SIZE AND DENSITY OF TITAN AEROSOL ANALOGS

The organic haze produced from complex CH{sub 4}/N{sub 2} chemistry in the atmosphere of Titan plays an important role in processes that occur in the atmosphere and on its surface. The haze particles act as condensation nuclei and are therefore involved in Titan's methane hydrological cycle. They also may behave like sediment on Titan's surface and participate in both fluvial and aeolian processes. Models that seek to understand these processes require information about the physical properties of the particles including their size and density. Although measurements obtained by Cassini-Huygens have placed constraints on the size of the haze particles, their densities remain unknown. We have conducted a series of Titan atmosphere simulation experiments and measured the size, number density, and particle density of Titan aerosol analogs, or tholins, for CH{sub 4} concentrations from 0.01% to 10% using two different energy sources, spark discharge and UV. We find that the densities currently in use by many Titan models are higher than the measured densities of our tholins.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A TENTATIVE SIZE-LUMINOSITY RELATION FOR THE IRON EMISSION-LINE REGION IN QUASARS

New reverberation mapping measurements of the size of the optical iron emission-line region in quasars are provided, and a tentative size-luminosity relation for this component is reported. Combined with lag measurements in low-luminosity sources, the results imply an emission-region size that is comparable to and at most twice that of the Hβ line, and is characterized by a similar luminosity dependence. This suggests that the physics underlying the formation of the optical iron blends in quasars may be similar to that of other broad emission lines.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Frictional properties of Opalinus Clay: influence of humidity, normal stress and grain size on frictional stability

SUMMARY The Opalinus Clay (OPA) is a clay-rich formation considered as a potential host rock for radioactive waste repositories and as a caprock for carbon storage in Switzerland. Its very low permeability (10−19 to 10−21 m2) makes it a potential sealing horizon, however the presence of faults that may be activated during the lifetime of a repository project can compromise the long-term hydrological confinement, and lead to mechanical instability. Here, we have performed laboratory experiments to test the effect of relative humidity (RH), grain size (g.s.) and normal stress on rate-and-state frictional properties and stability of fault laboratory analogues corresponding to powders of OPA shaly facies. The sifted host rock powders at different grain size fractions (<63 μm and 63 < g.s. < 125 μm), at room (∼25 per cent) and 100 per cent humidity, were slid in double-direct shear configuration, under different normal stresses (5–70 MPa). We observe that peak friction, μpeak and steady-state friction, μss, depend on water vapour content and applied normal stress. Increasing relative humidity from ∼25 per cent RH (room humidity) to 100 per cent RH causes a decrease of frictional coefficient from 0.41 to 0.35. The analysis of velocity-steps in the light of rate-and-state friction framework shows that the stability parameter (a–b) is always positive (velocity-strengthening), and it increases with increasing sliding velocity and humidity. The dependence of (a–b) on slip rate is lost as normal stress increases, for each humidity condition. By monitoring the variations of the layer thickness during the velocity steps, we observe that dilation (Δh) is directly proportional to the sliding velocity, decreases with normal stress and is unaffected by humidity. Microstructural analysis shows that most of the deformation is accommodated within B-shear zones, and the increase of normal stress (σn) promotes the transition from strain localization and grain size reduction to distributed deformation on a well-developed phyllosilicate network. These results suggest that: (1) the progressive loss of velocity dependence of frictional stability parameter (a–b) at σn > 35 MPa is dictated by a transition from localized to distributed deformation and (2) water vapour content does not affect the deformation mechanisms and dilation, whereas it decreases steady-state friction (μss), and enhances fault stability.

58 GEOSCIENCES↗
DOE OSTI2020

Incubation Temperature Affects Duckling Body Size and Food Consumption Despite No Effect on Associated Feeding Behaviors

Synopsis Developmental conditions can have consequences for offspring fitness. For example, small changes (<1°C) in average avian incubation temperature have large effects on important post-hatch offspring phenotypes, including growth rate, thermoregulation, and behavior. Furthermore, average incubation temperatures differ among eggs within the same nest, to the extent (i.e., >1°C) that differences in offspring phenotypes within broods should result. A potential consequence of within-nest incubation temperature variation is inequality in behaviors that could cause differences in resource acquisition within broods. To investigate this, we incubated wood duck (Aix sponsa) eggs at one of two ecologically-relevant incubation temperatures (35°C or 36°C), formed mixed-incubation temperature broods after ducklings hatched, and conducted trials to measure duckling behaviors associated with acquisition of heat (one trial) or food (three trials). Contrary to our predictions, we found no effect of incubation temperature on duckling behaviors (e.g., time spent occupying heat source, frequency of feeding bouts). However, we found evidence that ducklings incubated at the higher temperature consumed more food during the 1-h feeding trials, and grew faster in body mass and structural size (culmen and tarsus) throughout the study, than those incubated at the lower temperature. Apparent food consumption during the trials was positively related to culmen length, suggesting that differences in food consumption may be driven by structural size. This could result in positive feedback, which would amplify size differences between offspring incubated at different temperatures. Thus, our study identifies incubation temperature as a mechanism by which fitness-related phenotypic differences can be generated and even amplified within avian broods.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Compact galaxies and the size–mass galaxy distribution from a colour-selected sample at 0.04 < z < 0.15 supplemented by ugrizYJHK photometric redshifts

ABSTRACT The size–mass galaxy distribution is a key diagnostic for galaxy evolution. Massive compact galaxies are potential surviving relics of a high-redshift phase of star formation. Some of these could be nearly unresolved in Sloan Digital Sky Survey (SDSS) imaging and thus not included in galaxy samples. To overcome this, a sample was selected from the combination of SDSS and UKIRT Infrared Deep Sky Survey (UKIDSS) photometry to r < 17.8. This was done using colour–colour selection, and then by obtaining accurate photometric redshifts (photo-z) using scaled flux matching (SFM). Compared to spectroscopic redshifts (spec-z), SFM obtained a 1σ scatter of 0.0125 with only 0.3 per cent outliers (|Δln (1 + z)| > 0.06). A sample of 163 186 galaxies was obtained with 0.04 < z < 0.15 over $2300\, {\rm deg}^2$ using a combination of spec-z and photo-z. Following Barro et al. log Σ1.5 = log M* − 1.5log r50, maj was used to define compactness. The spectroscopic completeness was 76 per cent for compact galaxies (log Σ1.5 > 10.5) compared to 92 per cent for normal-sized galaxies. This difference is primarily attributed to SDSS ‘fibre collisions’ and not the completeness of the main galaxy sample selection. Using environmental overdensities, this confirms that compact quiescent galaxies are significantly more likely to be found in high-density environments compared to normal-sized galaxies. By comparison with a high-redshift sample from 3D-HST, log Σ1.5 distribution functions show significant evolution, with this being a compelling way to compare with simulations such as EAGLE. The number density of compact quiescent galaxies drops by a factor of about 30 from z ∼ 2 to log (n/Mpc−3) = − 5.3 ± 0.4 in the SDSS–UKIDSS sample. The uncertainty is dominated by the steep cut off in log Σ1.5, which is demonstrated conclusively using this complete sample.

Baldry, Ivan K.↗
DOE OSTI2021

Cosmological constraints from H ii starburst galaxy, quasar angular size, and other measurements

ABSTRACT We compare the constraints from two (2019 and 2021) compilations of H ii starburst galaxy (H iiG) data and test the model independence of quasar (QSO) angular size data using six spatially flat and non-flat cosmological models. We find that the new 2021 compilation of H iiG data generally provides tighter constraints and prefers lower values of cosmological parameters than those from the 2019 H iiG data. QSO data by themselves give relatively model-independent constraints on the characteristic linear size, lm, of the QSOs within the sample. We also use Hubble parameter [H(z)], baryon acoustic oscillation (BAO), Pantheon Type Ia supernova (SN Ia) apparent magnitude (SN-Pantheon), and DES-3 yr binned SN Ia apparent magnitude (SN-DES) measurements to perform joint analyses with H iiG and QSO angular size data, since their constraints are not mutually inconsistent within the six cosmological models we study. A joint analysis of H(z), BAO, SN-Pantheon, SN-DES, QSO, and the newest compilation of H iiG data provides almost model-independent summary estimates of the Hubble constant, $H_0=69.7\pm 1.2\ \rm {km\,s^{-1}\,Mpc^{-1}}$, the non-relativistic matter density parameter, $\Omega _{\rm m_0}=0.293\pm 0.021$, and lm = 10.93 ± 0.25 pc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The mass–size relation of luminous red galaxies from BOSS and DECaLS

We use the DECaLS DR3 survey photometry matched to the SDSS-III/BOSS DR12 spectroscopic catalogue to investigate the morphology and stellar mass-size relation of luminous red galaxies within the CMASS and LOWZ galaxy samples in the redshift range 0.2 < z < 0.7. The large majority of both samples is composed of early-type galaxies with De Vaucouleurs profiles, while only less than 20 per cent are late-type exponentials. We calibrate DECaLS effective radii using the higher-resolution CFHT/MegaCam observations and optimize the correction for each morphological type. By cross-matching the photometric properties of the early-type population with the Portsmouth stellar mass catalogue, we are able to explore the high-mass end of the distribution using a large sample of 322994 galaxies over 4380 deg 2 . We find a clear correlation between the sizes and stellar masses of these galaxies, which appears flatter than previous estimates at lower masses. The sizes of these early-type galaxies do not exhibit significant evolution within the BOSS redshift range, but a slightly declining redshift trend is found when these results are combined with z ~ 0.1 SDSS measurements at the high-mass end. The synergy between BOSS and DECaLS has important applications in other fields, including galaxy clustering and weak lensing.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Finite-size effects in lead scandium tantalate relaxor thin films

Large electromechanical effects in relaxor ferroelectrics are generally attributed to the collective response of an ensemble of correlated, nanometer-sized polar structures induced by chemical and charge disorder. Here, we study finite-size effects on such polar order (i.e., how it evolves when sample dimensions approach the polarization correlation length) in 7–70-nm-thick films of the relaxor ferroelectric PbSc 0.5 Ta 0.5 O 3 . Temperature-dependent polarization studies reveal a linear suppression of the polarization and nonlinearity associated with relaxor order as the film thickness decreases to ≈ 30 nm. Below this thickness, however, the suppression rapidly accelerates, and polarization is completely absent by film thicknesses of ≈ 7 nm, despite the continued observation of a broad peak in dielectric permittivity and frequency dispersion. Diffuse-scattering measurements reveal the diffuse-scattering symmetry, and analysis suggests the films have a polarization correlation length of ≈ 23 nm. Finally, taken together, it is apparent that reduction of sample size and the resulting distribution of polar structures drive suppression and eventual quenching of the electrical response of relaxors, which may be attributed to increasing dipole-dipole and dipole-interface interactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗