Realizing Enhanced Energy Storage and Hardness Performances in 0.90NaNbO3-0.10Bi(Zn0.5Sn0.5)O3 Lead-Free Ceramics

Relaxor behavior has been demonstrated responsible for excellent energy storage characteristics in dielectric materials owing to the fast polarization response, and an ultrahigh energy storage density can also be induced in NaNbO3 (NN)-based ceramics via combining antiferroelectric and relaxor features. Most of the existing reports lead-free dielectric ceramics, nevertheless, are still lacking of the relevant research among domain evolution and relaxor behavior. Herein, a novel lead-free solid solution, (1-x)NaNbO3-xBi(Zn0.5Sn0.5)O3 [xBZS, x = 0.05, 0.10, 0.15, and 0.20] ceramics are designed to further illustrate the above issues. Domain evolutions in xBZS ceramics confirm the contribution of relaxor behavior to the excellent energy storage characteristics, owning to fast polarization rotation based on the low energy barrier of polar nanoregions (PNRs). Consequently, a high energy storage density of 3.14 J/cm3 and energy efficiency of 83.30% are simultaneously available at 0.10BZS ceramics, together with the stabilities of energy storage properties in large temperature range (20-100 °C) and wide frequency range (1-200 Hz). Additionally, for practical applications, the 0.10BZS ceramics display a great discharge energy storage density (Wdis ~1.05 J/cm3), fast discharge rate (t0.9 ~60.60 ns), and high hardness (H ~5.49 GPa). These results indicate that this study may provide a considerable new light on the mechanism of high performance lead-free dielectric energy storage materials.

Wastewater Disposal Has Not Significantly Altered the Regional Stress State in Southern Kansas

Wastewater disposal is primarily responsible for the increased seismicity rate since ∼2013 in southern Kansas. Previous work that used shear-wave splitting (SWS) in southern Kansas interpreted an ∼90° temporal rotation in the fast polarization direction and attributed it to increased pore pressures resulting from fluid injection. However, this interpreted rotation coincided with a change in the stations used to make the SWS measurements. We investigate the temporal variability of fast azimuths in southern Kansas by making SWS measurements on earthquake families with similar source–receiver paths recorded on a stable local seismic network. We select high-quality SWS measurements by investigating the stability of results across 65 different frequency bands between 0.5 and 15 Hz. We find that the fast polarization direction in southern Kansas is relatively constant with an average east-northeast (∼N79°E) orientation between 2014 and 2017. Our fast polarization measurements are primarily a reflection of the maximum principal horizontal stress direction (SHmax). We observe a slight spatial change in SHmax to the northeast (∼N55°E) near the Nemaha ridge in Oklahoma. However, we do not observe any significant temporal rotation of SHmax or variation in delay time (i.e., crack density) in southern Kansas, contrary to the earlier study. The previously interpreted ∼90° rotation may either be a reflection of a very local stress change or a misinterpretation of SWS results potentially due to the use of inconsistent source–receiver paths. Our SWS measurements cover the period of peak wastewater disposal and seismicity rates and suggest an absence of significant temporal rotations in the local anisotropy and stress orientations associated with wastewater disposal.

Spatially Distinct Tectonic Zones across Oklahoma Inferred from Shear-Wave Splitting

To better understand relationships among crustal anisotropy, fracture orientations, and the stress field in Oklahoma and southern Kansas, we conduct shear-wave splitting analysis on the last 9 yr of data (2010–2019) of local earthquake observations. Rather than a predominant fast direction (ϕ), we find that most stations have a primary fast direction of polarization (ϕpri) and a secondary fast direction of polarization (ϕsec). At most stations, either the primary fast direction of polarization (ϕpri) or the secondary fast direction of polarization (ϕsec) is consistent with the closest estimated maximum horizontal stress (σHmax) orientation in the vicinity of the observation. The general agreement between fast directions of polarization (ϕ) and the maximum horizontal stress orientations (σHmax) at the regional level implies that the fast polarization directions (ϕ) are extremely sensitive to the regional stress field. However, in some regions, such as the Fairview area in western Oklahoma, we observe discrepancies between fast polarization directions (ϕ) and maximum horizontal stress orientations (σHmax), in which the fast directions are more consistent with local fault structures. Overall, the primary fast direction of polarization (ϕpri) is mostly controlled and influenced by the stress field, and the secondary fast direction of polarization (ϕsec) likely has some geologic structural control because the secondary direction is qualitatively parallel to some mapped north-striking fault zones. No significant changes in fast directions over time were detected with this technique over the 5 yr (2013–2018) of measurements, suggesting that pore pressure may not cause a significant enough or detectable change above the magnitude of the background stress field.

Caribbean slab dynamics beneath northwest South America from SKS and Local S splitting

<p>     The southernmost edge of the Caribbean (CAR) plate, a buoyant large igneous province, subducts shallowly beneath northwestern South America (NWSA) at a trench that lies northwest of Colombia. Recent finite frequency P-wave tomography results show a segmented CAR subducting at a shallow angle under the Santa Marta Massif to the Serrania de Perijá (SdP) before steepening while a detached segment beneath the Mérida Andes (MA) descends into the mantle transition zone. The dynamics of shallow subduction are poorly understood. Plate coupling between the flat subducting CAR and the overriding NWSA is proposed to have driven the uplift of the MA. In this study we analyze SKS shear wave splitting to investigate the seismic anisotropy beneath the slab segments to relate their geometry to mantle dynamics. We also use local S splitting to investigate the seismic anisotropy between the slab segments and the overriding plate. The data were recorded by a 65-element portable broadband seismograph network deployed in NWSA and 40 broadband stations of the Venezuelan and Colombian national seismograph networks.</p><p>     SKS fast polarization axes are measured generally trench-perpendicular (TP) west of the SdP but transition to trench-parallel (TL) at the SdP where the slab was imaged steepening into the mantle, consistent with previous studies. West of the MA the fast axis is again TP but transitions to TL under the MA. This second transition from TP to TL is likely due to mantle material being deflected around a detached slab under the MA. Local S fast polarization axes are dominantly TP throughout the study area west of the Santa Marta Massif and are consistent with slab-entrained flow. Under the Santa Marta Massif the fast axis is TL for reasons we do not yet understand.</p>

Upper-Crustal Seismic Anisotropy in the Cantabrian Mountains (North Spain) from Shear-Wave Splitting and Ambient Noise Interferometry Analysis

The upper-crustal anisotropy of the Cantabrian Mountains (North Spain) has been investigated using two independent but complementary methodologies: (a) shear-wave splitting and (b) ambient seismic noise interferometry. For this purpose, we have processed and compared seismic data from two networks with different scales and recording periods. The shear-wave splitting results show delay times between 0.06 and 0.23 s and spatially variable fast-polarization directions. We calculate that the anisotropic layer has a maximum effective thickness of around 7.5 km and an average anisotropy magnitude of between 4% and 8%. Consistently, our ambient noise observations point to an anisotropy magnitude between 4% and 9% in the first 10 km of the crust. Our results show a clear correlation between the fast directions from both methods and the orientations of the local faults, suggesting that the anisotropy is mainly controlled by the structures. Furthermore, in the west of the study area, fast-polarization directions tend to align parallel to the Variscan fabric in the crust, whereas to the east, in which the Alpine imprint is stronger, many fast directions are aligned parallel to east–west-oriented Alpine features.

Detailed Investigation of Seismic Anisotropy in the Upper Mantle of the Northern Aegean Region

<p>Seismic anisotropy studies can provide important constraints on geodynamic processes and deformation styles in the upper mantle of tectonically active regions. Seismic anisotropy parameters (e.g. delay time and fast polarization direction) can give hints at the past and recent deformations and can be most conventionally obtained through core-mantle refracted SKS phase splitting measurements. In order to explore the complexity of anisotropic structures in the upper mantle of a large part of the Aegean region, in this study, we estimate splitting parameters beneath 25 broad-band seismic stations located at NW Anatolia, North Aegean Sea and Greece mainland. To achieve this we employ both transverse energy minimization and eigenvalue methods. Waveform data of selected earthquakes (with M<sub>w</sub> ≥ 5.5; 2008-2018 and with epicentral distances between 85°–120°) were retrieved from Earthquake Data Center System of Turkey (AFAD; http://tdvm.afad.gov.tr/) and European Integrated Data Archive (EIDA; http://orfeus-eu.org/webdc3/). A quite large data set, the majority of which have not been studied before, were evaluated in order to estimate reliable non-null and null results. In general, station-averaged splitting parameters mainly exhibit the NE-SW directed fast polarization directions throughout the study area. These directions can be explained by the lattice-preferred orientation of olivine minerals in the upper mantle induced by the mantle flow related to the roll-back process of the Hellenic slab. We further observe that station-averaged splitting time delays are prone to decrease from north to south of the Aegean region probably changing geometry of mantle wedge with a strong effect on  the nature of mantle flow along this direction. The uniform distribution of splitting parameters as a function of back-azimuths of earthquakes refers to a single-layer horizontal anisotropy for the most part of the study area. However, back azimuthal variations of splitting parameters beneath most of northerly located seismic stations (e.g., GELI, SMTH etc.) imply the presence of a double-layer anisotropy. To evaluate this, we performed various synthetic tests especially beneath the northern part of study region. Yet, it still remains controversial issue due to the large azimuthal gap and thus requires further modelling which may involve the use of joint data sets.</p>