Structural Distortion-Modulated Magnetic and Dielectric Properties in Nonstoichiometric Yb2-xTi2O7-δ Pyrochlore.

Rare-earth titanate pyrochlores have attracted considerable attention for their unique magnetic frustration. Among those compounds, Yb2Ti2O7, a candidate for quantum spin ice, has been extensively studied in its magnetic ground state. However, works on its dielectric property and structure-property relationship lag far more behind. Here, by preparing and investigating nonstoichiometric Yb2-xTi2O7-δ (x = 0-0.15) ceramics, we demonstrate that the samples with x ≤ 0.05 maintain a single-pyrochlore phase, but the nonstoichiometry arouses significant structural distortion and increased oxygen vacancy. As a result, the ferromagnetism, indicated by a positive Curie-Weiss temperature, decreases almost linearly with increasing x value. Remarkably composition-dependent low-temperature dielectric relaxations have been observed. In addition, through introducing nonstoichiometry, the relaxor degree of dielectric behavior is enhanced, and the dielectric curve shows an altered shape. The origin of this dielectric relaxation is attributed to the increased structural distortion reflected by the changed bond length/angle, since there is no phase transition in 90-300 K. Our work gives a comprehensive view on the structural, magnetic, and dielectric properties of Yb2Ti2O7, which is instructive for further work on pyrochlores.

Impact of remote ischemic postconditioning on acute ischemic stroke in China: a systematic review and meta-analysis of randomized controlled trials.

OBJECTIVE: Acute ischemic stroke (AIS) is a significant health burden in China, affecting a sizable portion of the population. Conventional pharmacological treatments frequently fall short of desirable outcomes. Therefore, exploring alternative therapies is crucial. Remote ischemic postconditioning (RIPostC) is a noninvasive and cost-effective adjunctive therapy. This study aimed to investigate the efficacy and safety of RIPostC as an adjunctive therapy for AIS to inform clinical practice. METHODS: A comprehensive search was conducted across the PubMed, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), WanFang, Weipu (VIP), and China Biology Medicine disc (CBM) databases up to October 2023. All included studies underwent bias risk assessment using the Cochrane risk-of-bias assessment tool. The primary outcome measure was the National Institute of Health Stroke Scale (NIHSS), with secondary outcomes including the Barthel index (BI), D-dimer, C-reactive protein (CRP), fibrinogen (FIB), brain-derived neurotrophic factor (BDNF), modified Rankin scale (mRS), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) levels. The data were analyzed using fixed-effects and random-effects models in Review Manager, with mean differences (MDs) and 95% confidence intervals (CIs) calculated for each outcome. The grading of recommendations, assessment, development, and evaluations (GRADE) approach was used to evaluate the level of evidence for each outcome measure. RESULTS: This meta-analysis included 38 studies, encompassing 4334 patients. Compared with the control group, the RIPostC group had significantly lower NIHSS scores, serum CRP, D-dimer, IL-6, TNF-α, and FIB levels, and increased BDNF levels. Moreover, it improved the patient's BI and mRS scores. According to the GRADE approach, the quality of evidence for mRS was deemed "moderate," while the NIHSS, BI, and CRP were rated as "low" quality. IL-6, TNF-α, FIB, D-dimer, and BDNF received "very low" quality ratings. CONCLUSION: The findings suggest that RIPostC activates endogenous protective mechanisms, providing benefits to patients with AIS.

Significant effects of minor chemical composition changes on the structure and property of (Pb1-ySry)(Mg1/3Nb2/3)0.07ZrxTi0.93-xO3:zLa.

Piezoelectric ceramics with high electrical performances and high Curie temperature (Tc) act as key materials for numerous electromechanical devices such as transducers and actuators. Herein, we report a systematic investigation on the crystal structure, microstructure and electrical properties of Sr and La co-doped Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics with a low Pb(Mg1/3Nb2/3)O3 content, namely, (Pb1-ySry)(Mg1/3Nb2/3)0.07ZrxTi0.93-xO3:zLa. With an increase in the Zr content (x value) from 0.49 to 0.53, its crystal structure evolved from a tetragonal phase to a rhombohedral phase, leading to not only a morphotropic phase boundary (MPB) at around x = 0.51 but also a monotonously decreasing Tc. Meanwhile, a change in either the Sr- or La-doping content (y and z values, respectively) in the range of y = 0.03-0.07 and z = 0.01-0.03 can slightly deviate the structure of MPB, resulting in a significant effect on its electrical properties. As the best results, the optimal composition of x = 0.51, y = 0.05, and z = 0.02 yielded peak electrical performance, with a related room temperature piezoelectric coefficient (d33) of 645 pC N-1, remanent polarization (Pr) of 33.5 µC cm-2, coercive field (Ec) of 8.6 kV cm-1, and Tc of 242 °C. Especially, its piezoelectric properties showed excellent temperature stability, and its d33 value decreased by only 3% from room temperature to 150 °C. This work not only provides an alternative piezoelectric ceramic with outstanding electrical performance for industrial applications, but also reveals a comprehensive perspective on the composition-structure-property relationship of doped Pb[(Mg1/3Nb2/3),Zr,Ti]O3, which is helpful for further work on piezoelectric ceramics.

Nonvolatile Control of the Electronic Properties of In2-xCrxO3 Semiconductor Films by Ferroelectric Polarization Charge.

A series of Cr-doped In2-xCrxO3 (ICO) semiconductor thin films were epitaxially grown on (111)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29PT) single-crystal substrates by the pulsed laser deposition. Upon the application of an electric field to the PMN-0.29PT substrate along the thickness direction, we realized in situ, reversible, and nonvolatile control of the electronic properties and Fermi level of the films, which are manifested by abundant physical phenomena such as the n-type to p-type transformation, metal-semiconductor transition, metal-insulator transition, crossover of the magnetoresistance (MR) from negative to positive, and a large nonvolatile on-and-off ratio of 5.5 × 104% at room temperature. We also strictly disclose that both the sign and the magnitude of MR are determined by the electron carrier density of ICO films, which could modify the s-d exchange interaction and weak localization effect. Our results demonstrate that the ferroelectric gating approach using PMN-PT can be utilized to gain deeper insight into the carrier-density-related electronic properties of In2O3-based semiconductors and provide a simple and energy efficient way to construct multifunctional devices which can utilize the unique properties of composite materials.