Large Pr Research Articles

Scaling Law of Flow and Heat Transfer Characteristics in Turbulent Radiative Rayleigh-Bénard Convection of Optically Thick Media

Radiative natural convection is of vital importance in the process of energy storage, power generation, and thermal storage technology. As the attenuation coefficients of many heat transfer media in these fields are high enough to be considered as optically thick media, like nanofluids or molten salts in concentrated solar power or phase change thermal storage, Rosseland approximation is commonly used. In this paper, we delve into the impact of thermal radiation on the Rayleigh-Bénard (RB) convection. Theoretical analysis has been conducted by modifying the Grossmann-Lohse (GL) model. Based on turbulent dissipation theory, the corresponding scaling laws in four main regimes are proposed. Direct numerical simulation (DNS) was also performed, revealing that radiation exerts a notable influence on both flow and heat transfer, particularly on the formation of large-scale circulation. By comparing with DNS results, it is found that due to the presence of radiation, the modified Nu scaling law in small Pr range of the GL model is more suitable for predicting the transport characteristics of optical thick media with large Pr. The maximum deviation between the results of DNS and prediction model is about 10%, suggesting the summarized scaling law can effectively predict the Nu of radiative RB convection.

Improved piezoelectric performance in CBN-based ceramic through triple-doping (Li, Bi, Ce) strategy

Bismuth layered structural ferroelectrics (BLSFs) with high Curie temperature (TC) and low aging rate establish the groundwork for the advancement of high-temperature piezoelectric devices. CaBi2Nb2O9 (CBN) is an excellent candidate for possessing the highest TC value (∼940 °C) among BLSFs. However, its poor piezoelectricity impedes practical applications. Generally, the excellent piezoelectric properties of CBN-based ceramics depend on intrinsic and extrinsic contributions. Here, Aurivillius ferroelectrics with triple-doping ions, Ca1–2x(LiBi0.7Ce0.3)xBi2Nb2O9 (CBN-xLBC), were fabricated to achieve large piezoelectric constant (d33∼23.3 pC/N) and high Curie temperature (∼906 °C) simultaneously due to tetragonal distortion and smaller nanodomains. Besides, the DC resistivity of optimal sample is still above 1×105 Ω·cm at 600 °C. At the same time, the ferroelectricity is improved significantly with large Pr (∼18.9 μC/cm2) when x=0.275. The improved comprehensive performance of CBN-based ceramic indicates that proper various ions synergetic effect plays an important role and CBN-0.275LBC ceramic is expected to apply in practical industry.

Physical properties of Pr3+ substituted zinc spinel (ZnPrxFe2−xO4) nanoferrites synthesized via sol–gel auto-combustion route

Spinel ferrites, a group of metal oxides, have garnered significant attention in the recent decade due to their high demand for numerous applications, including data storage and microwave device applications. In this context, we studied the effect of different doping concentrations of large Pr ions on the physicochemical properties of spinel lattice, such as dielectric and magnetic properties. In this research, we successfully fabricated a series of praseodymium ion-doped zinc spinel ferrites ZnPrxFe2-xO4 nanoparticles 0.00≤x≤0.20 via a simple and economical sol–gel auto-combustion approach. XRD (X-ray Diffraction Analysis) and FTIR investigations validate the presence of a cubical phase, with the crystallite size varying between 11 nm to 19 nm depending on the amount of Pr present. The Scherrer method, Williamson-Hall analysis (WH), and size-strain plot method (SSP) were investigated the correlation of crystalize size. The SSP approach has a better correlation coefficient than the WH method. Transmission electron microscopy TEM shows that the prepared material possessed the cubic and spherical symmetry. The significant variation in electrical parameters was discussed at an applied frequency ranging from 1 MHz to 3 GHz. The dielectric constant is approximately constant in low-frequency regions then relaxation peaks were observed at nearly 1.4 GHz and 2.2 GHz. The dielectric constant and complex dielectric constant of these samples dropped as the praseodymium content increased. Investigations regarding the magnetic properties were carried out using a vibrating sample magnetometer (VSM) at −23 k Oe to +23 k Oe. Low coercivity and relaxation peaks at high frequencies suggest that this material may be suitable for core materials, microwave technologies and recording media.

Exact solution for heat transfer across the Sakiadis boundary layer

We consider the problem of convective heat transfer across the laminar boundary layer induced by an isothermal moving surface in a Newtonian fluid. In a previous work [Barlow et al., “Exact and explicit analytical solution for the Sakiadis boundary layer,” Phys. Fluids 36, 031703 (2024)], an exact power series solution was provided for the hydrodynamic flow, often referred to as the Sakiadis boundary layer. Here, we utilize this expression to develop an exact solution for the associated thermal boundary layer as characterized by the Prandtl number (Pr) and local Reynolds number along the surface. To extract the location-dependent heat transfer coefficient (expressed in dimensionless form as the Nusselt number), the dimensionless temperature gradient at the wall is required; this gradient is solely a function of Pr and is expressed as an integral of the exact boundary layer flow solution. We find that the exact solution for the temperature gradient is computationally unstable at large Pr, and a large Pr expansion for the temperature gradient is obtained using Laplace's method. A composite solution is obtained, which is accurate to O(10−10). Although divergent, the classical power series solution for the Sakiadis boundary layer—expanded about the wall—may be used to obtain all higher-order corrections in the asymptotic expansion. We show that this result is connected to the physics of large Prandtl number flows where the thickness of the hydrodynamic boundary layer is much larger than that of the thermal boundary layer. The present model is valid for all Prandtl numbers and attractive for ease of use.

P128 Predicting Persistent Inflammatory Arthritis in patients with Palindromic Rheumatism: Development of Scores for Risk Stratification

Abstract Background/Aims Palindromic rheumatism (PR) is a recognised precursor of rheumatoid arthritis (RA). Up to 50% of PR patients will progress to persistent inflammatory arthritis (PIA) but risk factors for progression remain unclear. Analysis of this large UK prospective PR cohort has been used to develop the first risk stratification tool to predict progression to PIA. Methods The Leeds PR cohort was recruited from regional primary and secondary care referrals. PR was defined as ‘a confirmed history/physical examination consistent with episodes of joint pain and swelling that returned to normal in the absence of an alternative diagnosis’. Clinical, serological and immunogenetic parameters were assessed at baseline and three monthly for the first year, then six monthly. Progression to PIA was defined as clinical synovitis persisting for >3 weeks as confirmed by a rheumatologist. Prediction models were developed by performing a Cox regression analysis, then applying LASSO to select the most important risk variables (using R). Results 161 PR patients were followed between July 2008 and January 2023. 33% (53/161) developed PIA and 91% of progressors met criteria for RA. 90% of patients were DMARD naive at baseline. Female gender, anti-cyclic citrullinated peptide (anti-CCP) positivity, rheumatoid factor (RF) positivity, age>40, smoking (ever) and a typical interval between attacks of < 1 month were all associated with progression (Table 1). Cox regression analysis showed female gender (HR 2.2CI1.1-4.7, p = 0.03) and anti-CCP>3x upper limit of normal (HR 5.9, CI 2.0-17.4, p = 0.002) were strongly associated with progression. 'Ever’ and 'Two-year’ prediction models were created to calculate risk of developing PIA (Table 1). Patients could be stratified into high, moderate and low risk groups, with progression rates of 53% (34/64), 25% (19/77) and 0% respectively in the ‘Ever’ model and 37% (27/ 73), 16% (11/69) and 0% respectively in the ‘Two-year’ model. Conclusion In patients with PR, female gender, positive anti-CCP, positive RF, age >40, smoking and a typical interval between attacks of < 1 month were predictive of progression to PIA. Combining these factors allows feasible risk stratification in clinical practice. High and moderate risk groups should be monitored in secondary care and considered for interventional trials. Disclosure R. Chowdhury: None. F. Shuweihdi: None. N. Sidhu: None. L. Duquenne: None. L. Garcia-Montoya: None. J. Nam: None. A. Di Matteo: None. K. Harnden: None. D. Sahin-Eroglu: None. P. Emery: Consultancies; BMS, AbbVie, MSD, Pfizer, Novartis, and Roche. Honoraria; Abbvie, Gilead, Lilly, Novartis. Grants/research support; AbbVie, BMS, Lilly, Samsung. K. Mankia: Honoraria; Abbvie, Lilly, UCB, Galapagos. Grants/research support; Gilead, Lilly.

Scalable ferroelectricity of 20 nm-thick (Al0.8Sc0.2)N thin films sandwiched between TiN electrodes

Ferroelectric (Al, Sc)N thin films have the potential for use in low-power memory applications. This study demonstrates the thickness scalability of ferroelectricity down to an approximately 20 nm-thick (Al0.8Sc0.2)N film sandwiched between microfabricable TiN electrodes. The impact of the deposition gas atmosphere during the sputtering process and the top electrode materials on the crystal structures and ferroelectric properties was investigated for 20–30 nm-thick (Al0.8Sc0.2)N thin films deposited on Si substrates covered with a TiN layer by radio frequency magnetron sputtering. The deposition atmosphere did not strongly affect the crystal structures of the 30 nm-thick (Al0.8Sc0.2)N films but significantly affected their ferroelectric properties. The leakage current density decreased for films deposited under pure N2 gas compared to the films deposited under a gas mixture of 0.67Ar + 0.33N2. The ferroelectric properties of 20 nm-thick (Al0.8Sc0.2)N films were changed by the top electrode materials; both the switching electric field and its maximum applicable electric field increased for the TiN top electrodes compared with the Pt top electrodes, improving the saturation characteristics of the remnant polarization (Pr) against the applied electric field. Consequently, the 20 nm-thick (Al0.8Sc0.2)N film sandwiched between the microfabricable TiN top and bottom electrodes showed ferroelectricity without noticeable degradation with decreasing film thickness; the film maintained large Pr values of over 100 μC/cm2 in the temperature range from room temperature to 150 °C. The present data open the door to scalable ferroelectric random-access memories using almost thickness-degradation-free thin (Al, Sc)N films with microfabricable TiN electrodes.

Comparison of different laryngeal preservation strategies based on chemoradiotherapy in locally advanced hypopharyngeal carcinoma

Objective:This study aimed to evaluate the clinical features and treatment outcomes of the value of response-adapted treatment following radiotherapy and induction chemotherapy follwing subsequent comprehensive therapy in patients with resectable locally advanced hypopharyngeal carcinoma. Methods:This cohort study was conducted from September 2010 to September 2020 in our hospital, 231 patients pathologically confirmed stage Ⅲ and ⅣB resectable locally advanced hypopharyngeal carcinoma included. For the IC-directed ART strategy, IC is used to select good candidates to receive radical RT or CCRT, and others undergo surgery. He response-adapted strategy was determined based on the primary tumor response, which was evaluated at a dose of 50 Gy. If the response reached complete response or partial response（more than 80% tumor regression）, patients received radical RT or CCRT; otherwise, they received surgery, if possible, at 4 to 6 weeks after RT. The end points of the study were OS（overall survival）, progression free survival（PFS）, locoregional recurrence-free survival（LRRFS） and LDFS. Results:In IC-directed group, 75.0%（57/76） patients reached PR after 2 cycles of induction chemotherapy. While in RT-directed group, 70.3%（109/155） patients reached large PR at dose of 50 Gy. The median interquartile range follow-up period of the whole cohort was 63.8 months. The 5-year OS, PFS, LRRFS and SFL of the whole cohort were 47.9%、39.6%、44.3% and 36.2%, respectively. In evaluations based on the different treatment strategies, the 5-year OS and SFL were 51.3% versus 37.0%（HR 0.67; 95%CI 0.43-1.05; P=0.07） and 27.8% versus 39.8%（HR 0.68; 95%CI 0.46-0.99; P=0.04） between IC-directed and RT-directed groups. In additional, surgery complications did not significantly differ between these two groups. Conclusion:In this cohort study, the response-adapted strategy based on an early RT response facilitated better treatment tailoring, and higher laryngeal preservation compared with IC-directed strategies. This approach could provide a feasible laryngeal preservation strategy in patients with resectable locally advanced hypopharyngeal carcinoma.

Large ferroelectric polarization of pure xBiFeO3-(1−x)BaTiO3 solid solution ceramics synthesized by microwave sintering

BiFeO3-BaTiO3 (BFO-BTO)-based lead-free electroceramics have long been synthesized using the microwave sintering approach, but the resulting multiferroic performance has not been excellent. In this work, we report an attempt to achieve competitive ferroelectric properties in microwave-sintered xBFO-(1–x)BTO (x = 0.6–0.8) ceramics. Adopting a sintering process with a short dwell time of 30 min at 970 °C, we obtain high-quality ceramics with a high density, pure perovskite structure, uniform element distribution, and coarse grains. Furthermore, the fabricated ceramics can reproduce the typical characteristics of pure BFO-BTO, including a morphotropic phase boundary (MPB), relaxor ferroelectric behavior, weak ferromagnetism, and enhanced ferroelectricity near the MPB. More remarkably, a large intrinsic remnant polarization Pr as high as ∼28 μC/cm2 is achieved by combing the MPB-enhanced ferroelectricity and the advantages of microwave synthesis. The maximal Pr accomplished here is competitive with that of the same bulk solid solution obtained via other fabrication approaches. Our study illustrates that microwave synthesis is a powerful approach with which to prepare high-performance BFO-BTO-based ceramics.

Multiple Local Domain Structural Evolutions at Morphotropic Phase Boundary in BiFeO3–Ba0.9Ca0.1TiO3 Ferroelectric Ceramics

Bismuth ferrite–barium titanate (BFO–BT) is a well‐known lead‐free ferroelectric material with a large electric field‐induced strain; however, its piezoelectricity is very low under low electric fields. Herein, by studying Ca‐doped BFO–BT ceramics, multiple structural evolutions are found in the ferroelectric domains at the morphotropic phase boundary (MPB) in BFO–BT‐based ceramics, where a part of the local ferroelectric domains reveals a transition from rhombohedral to tetragonal and to relaxor phases. The superior electrical properties with large electrostrain Sp of 0.38%, large Pr of 38.4 μC cm−2, intermediate d33 of 132 pCN−1, and high TC of 425 °C are obtained at the MPB in these ceramics. Multiple local domain structural evolutions with compound ferroelectric domains and relaxor phases are responsible for the large electrostrain and intermediate piezoelectricity. This can explain the inconsistent piezoelectric response under high and low electric fields at the MPB in the BFO–BT‐based ferroelectric ceramics.

Low-Dose and Stable X-ray Detection Enabled by Ferroelectric Perovskite Oxides

Ferroelectric perovskites are recognized as promising candidates for use in optoelectronics due to the efficient electron and hole extraction enabled by the spontaneous electric polarization induced depolarization electric field. Ferroelectric perovskite oxides also show good stability in harsh chemical, mechanical, and thermal conditions and can be fabricated by using robust and scalable methods. However, the small photocurrent of the typical ferroelectric oxide optoelectronics greatly limits their applications, such as in photovoltaics and photocatalysis. Here, we show that ferroelectric perovskite oxides are suitable for low-dose X-ray detection (ultraweak radiation detection). Ferroelectric plate-like perovskite-type CaBi2Ta2O9 (CBTa), prepared by a solid-state sintered reaction method, displays a spontaneous polarization (Ps) of 6.5 μC cm–2, a remanent polarization (Pr) of 4.9 μC cm–2, and a high Curie temperature (Tc) of 1196 K. Large resistivity and high Pr of CBTa enable a good response to low-dose X-rays under zero bias, resulting in a detection limit of 30 nGyair s–1 for the detector, which is much lower than the requirement for X-ray diagnostics (5.5 μGyair s–1). The CBTa detectors also exhibit ultralow noise and good operation stability. This study will motivate new strategies to explore low-dose and stable X-ray detectors with ferroelectric oxides.

Ferroelectric and piezoelectric properties of BaTiO3-templated 0.36BiScO3-0.64PbTiO3 thick films for piezoelectric device applications

ABSTRACT A novel 0.36BiScO3-0.64PbTiO3 (0.36BS-0.64PT) textured ceramic was developed using plate-like BaTiO3 (BT) templates for high temperature piezoelectric device applications. Sintering temperature and amount of BT template played important roles in improving the density, crystal orientation, and ferroelectric and piezoelectric properties of the BT-templated 0.36BS-0.64PT thick films. When sintered at 1000°C, highly dense BS-PT textured films were obtained without formation of a secondary phase. The increased amount of BT template facilitated the degree of texture but deteriorated the relative density of BS-PT thick film. In particular, enhanced ferroelectric and piezoelectric properties were obtained for 1 vol% BT-templated 0.36BS-0.64PT thick film sintered at 1000°C; this film exhibited the very large Pr (44.2 μC/cm2 at 4 kV/mm), d33 (444 pC/N), kp (57.4%), and g33 (36 × 10−3Vm/N) values. In addition, considering the inverse relation between TC and strain, the electrostrain of d33* (622 pm/V at 4 kV/mm) was excellent, showing potential for piezoelectric actuator applications.

Influence of crust formation on the heat load to a reactor vessel under an in-vessel retention condition

The heat load imposed on a reactor vessel was measured with and without the crust layer under an IVR-ERVC condition. Mass transfer experiments were performed based on heat and mass transfer analogy to achieve high RaʹH of order 1015 with compact test rigs. Geometric configuration and thermal boundary condition of the oxide pool due to crust formation were modeled. The results showed larger Nuup and lower Nudn than existing studies, which is due to the large Pr of the current experimental condition. The angular heat flux to the vessel increased monotonously with the angle regardless of the crust formation. Once the crust layer is formed, the thermal boundary condition near the vessel becomes melting temperature of the crust, which reduces the system temperature difference. The decreased buoyancy results in the decrease in both upward and downward heat transfers but the variation of the crust thickness did not show notable effect.

Response-Adapted Strategy Based on Early Response to Radiotherapy Achieves Favorable Survival With Functional Larynx in Resectable, Locally Advanced Hypopharyngeal Cancer: An Analysis of 423 Real-World Cases

The survival and larynx preservation were both important in hypopharyngeal cancer. For primary surgery, most patients need total laryngectomy. For primary radical concurrent chemoradiotherapy (CCRT), the non-responders to CCRT had worse outcome compared with surgery. Thus, our cancer center explored a new response-adapted strategy based on early response to radiotherapy.A total of 423 patients with resectable, III/IVA hypopharyngeal cancer were reviewed between May 2009 and October 2019. There were three main treatment strategies for locally advanced hypopharyngeal carcinoma in our institution, surgery followed by radiotherapy (S+RT group), response-adapted group and radical CCRT/RT (CRT group). The response-adapted strategy was determined by primary tumor regression evaluated at DT 50 Gy, only primary lesions reaching large PR were recommended for radical CCRT, otherwise planned surgery. We defined the survival with functional larynx as total laryngectomy or death from local disease.With a medial follow-up of 66.5 months, the 5-year overall survival (OS), locoregional recurrence-free survival (LRRFS), distance metastasis free survival (DMFS) and survival with functional larynx were 49.5%, 45.7%, 47.0% and 52.5% for whole cohort. For different groups, the 5-year OS, LRRFS, DMFS and survival with functional larynx were 54.4%, 52.5%, 52.3% and 47.4% for S+RT group (n = 144); 52.7%, 47.0%, 49.5% and 58.6% for response-adapted group (n = 212); 27.7%, 28.6%, 26.3% and 41.3% for CRT group (n = 67). The response-adapted strategy achieved similar survival and better survival with functional larynx compared with S+RT group, but the baseline between them were unbalanced. We use PSM to balance the two arms, the adjusted 5-year OS, LRRFS and DMFS were 54.8%, 48.7%, 53.5% for response-adapted group vs 52.2% 50.8%, 50.8% for S+RT group, without significant difference. But the adjusted 5-year larynx preservation rate and survival with functional larynx in response-adapted group were 75.1% and 53.8%, better compared with 56.1% and 50.1% in S+RT group (P < 0.01). The operative complications and acute toxicities (P > 0.05) for two groups had no difference. In subgroup analysis, 87.7% (186/212) required total laryngectomy when evaluated before treatment in the response-adapted group, but the 5-year survival with functional larynx were still 57.4%. In multivariable analysis, treatment strategies, ECOG, T and N stage were independently significant for OS, LRRFS, DMFS and survival with functional larynx.The response-adapted strategy achieved favorable survival with functional larynx and equally oncologist outcome compared with S+RT strategy. Besides, the response-adapted strategy did not result in additional operative complications and was well tolerated. Therefore, the response-adapted strategy might be an innovative, desirable for locally advanced hypopharyngeal cancer, especially for those with organ preservation intention.

Structure and properties of Bi(Zn½Ti½)O3‐modified Pb(Zr,Ti)O3 piezo‐/ferroelectric ceramics around the ternary morphotropic phase boundary

AbstractTo develop high‐performance piezo‐/ferroelectric materials, Bi(Zn½Ti½)O3–PbZrO3–PbTiO3 (BZT–PZ–PT) ternary solid solution with compositions around the morphotropic phase boundary (MPB) is synthesized by solid‐state reaction. The crystal structure and electric properties are investigated systematically by X‐ray powder diffraction (XRD), dielectric spectroscopy, and ferroelectric and piezoelectric measurements. On the basis of the results of the XRD, dielectric and ferroelectric measurements, the pseudo‐binary phase diagram of the yBi(Zn½Ti½)O3–(1 − y)[(1 − x)PbZrO3–xPbTiO3] system has been constructed for three series, namely, y = 0.05, 0.10, and 0.15. It is found that the introduction of BZT into the PZT system makes the paraelectric to ferroelectric phase transition more diffuse, brings the MPB to a lower PT content, and enlarges the MPB region. The best properties with an improved dielectric constant ε' = 1248, and a large remnant polarization Pr = 33 μC/cm2, as well as a relatively high TC = 286°C, and a high coercive field Ec = 23 kV/cm was achieved in the y = 0.15 series with MPB composition x = 0.425, making it a promising material for high‐power piezoelectric applications.

Maximizing and minimizing the boundary scattering mean free path in diameter-modulated coaxial cylindrical nanowires

The thermal conductivity (k) of semiconducting nanomaterials is influenced by the geometry-dependent phonon boundary scattering mean free path (ΛBdy). Although prior work has calculated ΛBdy of periodically corrugated rectangular nanowires and used these results to study phonon backscattering in nanomaterials, ΛBdy remains unknown for recently fabricated periodic coaxial cylindrical nanowires. Here, we use phonon ray tracing simulations to comprehensively study the effect of geometric parameters on ΛBdy in coaxial cylindrical nanowires. We find that for a fixed smaller cylinder diameter (D1) and cylinder length ratio, ΛBdy of periodic nanowires can be maximized or minimized via geometric control of the pitch (p) and larger cylinder diameter (D2). Our simulations show that saturated phonon backscattering for small pitch ratio (pr) nanowires gives rise to a minimum in ΛBdy/D1 at pr near unity, while the maximum in ΛBdy/D1 for large pr nanowires can be understood using a simple thermal resistor model for two individual nanowires in series. Combining our ΛBdy calculations with analytical phonon dispersion and bulk scattering models, we predict that k of periodic silicon nanowires with fixed D1can be tuned by up to 34% in the boundary scattering dominated regime by modifying D2 and p and that variations as large as 135% can be observed in the normalized thermal conductance. Our results provide insight into geometry-dependent phonon backscattering and can be used to predict k of periodic cylindrical nanowires over a range of temperatures and geometric lengthscales.

Scale of plume clustering in large-Prandtl-number convection.

Clustering of plumes in turbulent Rayleigh-Bénard convection has been numerically observed in low-Prandtl-number fluids. In this framework, turbulent plumes undergo a phase-separation process leading to large-scale clusters and circulations, sometimes called plume superstructures and reminiscent of solar granulation and supergranulation. On the other hand, the possible presence of large-scale plume aggregates has not been explored in the case of large values of the Prandtl number, Pr, relevant to geological settings such as convection in planetary interiors. Here we address this problem and numerically explore the behavior of plume ensembles in turbulent convection at very high Prandtl number values, including the case Pr→∞. The results indicate the presence of plume clustering, albeit at smaller scale, also for large Pr number fluids, suggesting interesting consequences for mantle convection processes.

Instabilities of thermocapillary liquid layers with two free surfaces

The instabilities of thermocapillary liquid layers with two free surfaces are examined by linear stability analysis. The surface tension is big enough to keep the liquid surfaces non-deformable. The effect of vertical temperature difference between two interfaces (Q) is considered. The critical parameters of preferred modes are determined, which depend on the Prandtl number (Pr) and Biot number (Bi). When Q=0, the preferred modes are the oblique wave at small Pr and the streamwise wave at large Pr. The perturbation is symmetric and anti-symmetric at small and large Pr, respectively. When Q>0, the preferred mode changes from the oblique wave to the streamwise wave, and finally the spanwise stationary mode with the increase of Pr. The instability mechanism is discussed. Comparisons are made with the liquid layer with a single free surface and previous results by numerical simulations and experiments.

Enhanced Energy-Storage Density by Reversible Domain Switching in Acceptor-Doped Ferroelectrics

Typical ferroelectrics possess a large spontaneous polarization Ps but simultaneously a large remnant polarization Pr as well, resulting in an inferior energy storage density.A mechanism that can reduce the Pr while maintain the Ps is demanded to enhance the energy storage property of ferroelectrics.In the present study, it is shown that after acceptor doping and aging treatment, the domain switching in ferroelectrics becomes reversible, giving rise to a pinched double hysteresis loop. The pinched loop with a large Ps and a small Pr thus results in an enhanced energy storage density. The physics behind is a defect induced internal field that provides a restoring force for the domains to switch back.The idea is demonstrated through a time-dependent Ginzburg-Landau simulation as well as experimental measurements in BaTiO$_3$ based single crystal and ceramics. The mechanism is general and can be applied to various ferroelectrics, especially the environment-friendly ones.

The response to external excitations in thermocapillary liquid layers

The responses to external excitations in thermocapillary liquid layers are investigated by non-modal stability theory. The maximum amplification of input signals is measured by a response function depending on the perturbation velocity and temperature. There can be rather large amplifications in subcritical flows at both small and large Prandtl numbers (Pr). For small Pr, the response increases significantly with both the Reynolds number (R) and the Biot number (Bi) but decreases with Pr. The optimal response is achieved when the perturbation is almost a spanwise wave. The response properties for the linear flow and the return flow are similar. The amplification is caused by a combination of the lift-up mechanism, Orr mechanism, and external forcing. However, for large Pr, large amplifications could only be found in the return flow, while the variations of response with Pr and Bi are opposite to those at small Pr. The optimal response propagates in the streamwise direction. The amplification is caused by the thermocapillary effect.

Effects of TiN Top Electrode Texturing on Ferroelectricity in Hf1-xZrxO2.

Ferroelectric memories based on hafnium oxide are an attractive alternative to conventional memory technologies due to their scalability and energy efficiency. However, there are still many open questions regarding the optimal material stack and processing conditions for reliable device performance. Here, we report on the impact of the sputtering process conditions of the commonly used TiN top electrode on the ferroelectric properties of Hf1–xZrxO2. By manipulating the deposition pressure and chemistry, we control the preferential orientation of the TiN grains between (111) and (002). We observe that (111) textured TiN is superior to (002) texturing for achieving high remanent polarization (Pr). Furthermore, we find that additional nitrogen supply during TiN deposition leads to >5× greater endurance, possibly by limiting the scavenging of oxygen from the Hf1–xZrxO2 film. These results help explain the large Pr variation reported in the literature for Hf1–xZrxO2/TiN and highlights the necessity of tuning the top electrode of the ferroelectric stack for successful device implementation.