RESUMO
Dielectric ceramic capacitors are highly regarded for their rapid charge-discharge, high power density, and cyclability in various advanced applications. However, their relatively low energy storage density has prompted intensive research aiming at developing materials with a higher energy density. To enhance energy storage properties, research has focused on modifying ferroelectric materials to induce relaxor ferroelectricity. The present study aims to induce a superparaelectric (SPE) state in relaxor ferroelectrics near room temperature by altering BaTiO3 ferroelectric ceramics using the (Sr,Bi)TiO3-Bi(Mg0.5Ti0.5)O3 system ((1-x)BT-x(SBT-BMT)). X-ray diffraction and Raman spectroscopy analysis demonstrated a shift in the crystal structure from tetragonal to cubic with an increasing x content. Notably, the compositions (except x = 0.1) satisfied the criteria for the SPE state manifestation near room temperature. The x = 0.2 specimen displayed characteristics at the boundary between the relaxor ferroelectric and SPE phases, while x ≥ 0.3 specimens exhibited increased SPE state fractions. Despite reduced maximum polarization, x ≥ 0.3 specimens showcased impressive energy storage capabilities, attributed to the enhanced SPE state, especially for x = 0.3, with impressive characteristics: a recoverable energy density (Wrec) of ~1.12 J/cm3 and efficiency (η) of ~94% at 170 kV/cm applied field. The good stability after the charge-discharge cycles reinforces the significance of the SPE phase in augmenting energy storage in relaxor ferroelectric materials, suggesting potential applications in high-energy density storage devices.
RESUMO
This study investigated the causes of microstructural changes and the resultant electrical properties according to the sintering temperature of 0.96(K0.46-xNa0.54-x)Nb0.95Sb0.05O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 lead-free ceramics by analyzing the correlation between vacancy concentrations and 2D nucleation. When sintered for 4 h, no grain growth occurred for the x = 0.000 composition over a wide temperature range, demonstrating that the existence of initial vacancies is essential for grain growth. As x increased, that is, as the vacancy concentration increased, the critical driving force (ΔGC) for 2D nucleation decreased, and abnormal grain growth was promoted. The number and size of these abnormal grains increased as the sintering temperature increased, but at sintering temperatures above 1100 °C, they decreased again owing to a large drop in ΔGC. The x = 0.005 specimen sintered at 1085 °C exhibited excellent piezoelectric properties of d33 = 498 pC/N and kp = 0.45 due to the large number of large abnormal grains with an 83% tetragonal phase fraction. The x = 0.000 specimen sintered at 1130 °C with suppressed grain growth exhibited good energy storage properties because of its very high relative density and small grain size of 300 to 400 nm.
RESUMO
The objective of this study was to evaluate the efficacy and safety of gemigliptin added to a stable dose of insulin alone or of insulin in combination with metformin in patients with type 2 diabetes mellitus. After a two-week run-in period, patients were randomized 2:1 to receive gemigliptin 50 mg or placebo once daily as add-on to background therapy with insulin or insulin plus metformin for 24 weeks. The primary endpoint was change in haemoglobin A1c (HbA1c) from baseline at Week 24. Baseline characteristics were similar between the gemigliptin (n = 188) and placebo (n = 95) groups in terms of HbA1c (8.1%). At Week 24, the gemigliptin group showed a statistically significant reduction in mean HbA1c from baseline as compared with placebo (between-group mean difference, -0.7% [95% CI, -0.9% to -0.4%]; P-value < 0.0001). The incidence of overall adverse events and the number of hypoglycaemic adverse events were similar between the study groups. Gemigliptin added to insulin alone or to insulin in combination with metformin resulted in superior glycaemic control compared to that in the placebo group and was well tolerated for 24 weeks in patients with type 2 diabetes mellitus, without causing weight gain or increasing the incidence of hypoglycaemia.
