Search

In this study, a series of (Ba 0.95 Ca 0.05 )(Ti 0.90 Sn 0.10 )O 3 – x LiF (BCTS– x LiF) (0≤ x ≤6 mol%) lead-free piezoceramics were fabricated by a conventional solid-state reaction method. The incorporation of LiF could significantly improve the sinterability of BCTS ceramics by reducing the sintering temperature from 1480 °C to 1250 °C, where a relative density over 90% was achieved with grown grains of 5–20 μm. X-ray diffraction and Raman spectroscopy experiments revealed that BCTS– x LiF ceramics are composed of coexisting R – O – T phases at 0≤ x ≤1 and R – T phases at 2≤ x ≤6 at room temperature. Optimal piezoelectric properties of d 33 =510 pC/N, k p =40.9%, ε r =5370, tan δ =0.019 and d S /d E =961 pm/V were obtained at x =5, which is attributed to the coexistence of R and T phases with an optimum ratio at room temperature and dense structure with large grains. [ABSTRACT FROM AUTHOR]

A high piezoelectricity enhancement achieved in (Ba,Ca)(Ti,Sn)O 3 lead-free ceramics sintered with 4 mol% Li 2 O additives by intensifying effect of sintering temperature ( T S ) in a wide interval (1300–1450 °C) has been found to be related to both the point defects and phase structures. X-ray photoelectron spectroscopy confirmed a reduction of tetravalent cations in B-sites to lower valence state such as Ti 3+ and Sn 2+ along with an increased content as raising T S . Photoluminescence spectra indicated higher oxygen vacancy concentrations as T S is too low or too high than those at an intermediate T S range, which is attributed to the volatilization of Li + and the inadequate oxygen supply in environment at high T S . Owing to coexisting rhombohedral and tetragonal phases at room temperature, a high piezoelectric coefficient d 33 up to 578 pC/N was achieved as T S =1350 °C. [ABSTRACT FROM AUTHOR]

This work investigated the enhanced sintering and electrical properties of (Ba 0.95 Ca 0.05 )(Ti 0.90 Sn 0.10 )O 3 - x Li 2 O (BCTSLi x , x = 0, 1, 2, 3, 4, 5 and 6 mol%) lead-free piezoelectric ceramics benefiting from the Li 2 O addition. Highly dense BCTS ceramics with good piezoelectric properties were fabricated at reduced sintering temperatures by adding a small amount of Li 2 O. It was found that the sintering densification is promoted mainly by reaction liquid phase at the early sintering stage and the formation of oxygen vacancies should be considered as an additional factor. The coexistence of R and T phases was confirmed by the Raman spectrum at a temperature range from−50 °C to 40 °C as x = 2 and at room temperature for all other Li 2 O added samples, while their specific ratio of R to T phase decreases with increasing Li 2 O addition. Better properties with d 33 = 457 pC/N, k p = 25.18% and Q m = 491 were obtained when adding 4 mol% Li 2 O, which are attributed dominantly to the appropriate specific ratio of R to T phase because of the similar grain size and density for samples at 3 ≤ x ≤ 6. [ABSTRACT FROM AUTHOR]

Abstract: The total syntheses of norartocarpin and artocarpin, two biologically interesting natural flavonoids with two regioisomeric isoprenyl side chains, were achieved for the first time via a linear reaction sequence of 9 and 12 steps with the overall yields of 14% and 3.5%, respectively, starting from commercially available 1,3,5-trimethoxybenzene. [Copyright &y& Elsevier]

Abstract: The polymorphic phase transition (PPT) from tetragonal to orthorhombic symmetry was tailored in lead-free piezoelectric ceramics Li0.08(Na0.52+x K0.48)0.92NbO3 (LN0.52+x KN) by controlling excess Na content, which is opposite to the usually reported orthorhombic–tetragonal phase transition. The grain growth was accelerated by adding excess Na, resulting in an increased grain size from 2–3μm to 7–8μm and a bimodal grain size distribution for samples x=0.015–0.04. The optimized piezoelectric properties with, i.e. d 33=226pC/N and k p=36.8% were obtained in sample x=0.04 due to the PPT effect. The corresponding T C, P r, and E r were 468°C, 25.5μC/cm2 and 1.20kV/mm, respectively. [Copyright &y& Elsevier]