Yinmei Lu

High recoverable energy density over a wide temperature range in Sr modified (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics with an orthorhombic phase

Via incorporation of Sr2+ into (Pb,La)(Zr,Sn,Ti)O3, high recoverable energy density (Ure) is achieved in (Pb,Sr,La)(Zr,Sn,Ti)O3 (PSLZST) ceramics. All Sr2+ modified ceramics exhibit orthorhombic antiferroelectric (AFE) characteristics, and have higher ferroelectric-AFE phase switching electric field (EA, proportional to Ure) than the base composition with a tetragonal AFE phase. By properly adjusting the Sr2+ content, the Ure of PSLZST ceramics is greatly improved. This is attributed to the substitution of Pb2+ by Sr2+ with a smaller ion radius, which decreases the tolerance factor leading to enhanced AFE phase stability and thus increased EA. The best energy storage properties are achieved in the PSLZST ceramic with a Sr2+ content of 0.015. It exhibits a maximum room-temperature Ure of 5.56 J/cm3, the highest value achieved so far for dielectric ceramics prepared by a conventional sintering technique, and very small energy density variation ( 4.9 J/cm3) over ...

The Effects of Ta Substitution and K/Na Ratio Variation on the Microstructure and Properties of (K,Na)NbO3-Based Lead Free Piezoelectric Ceramics

Abstract[(Na0.5+yK0.5−y)0.94Li0.06][(Nb0.94Sb0.06)1−xTax]O3 + 0.08 mol% MnO2 lead-free piezoelectric ceramics were fabricated successfully by a conventional solid-state reaction method. The effects of Ta5+ substitution and K/Na ratio variation on the microstructure and properties of the ceramics have been systematically investigated. With the increasing of Ta5+ substitution content, the orthorhombic–tetragonal transition temperature To–t presents obvious “V” type variation while the Curie temperature Tc decreases monotonically. The ceramics properties were further enhanced by adjusting the Na/K ratio of the A-site. Under systematical optimization of the A-site and B-site elements, good overall electrical properties of d33 = 276 pC/N, kp = 44.5%, ε33T/ε0 = 1,175, tanδ = 0.027, Tc = 309 °C, Pr = 21.0 μC/cm2, and Ec = 1.14 kV/mm were obtained for ceramics with Ta5+ content x of 0.05 and Na/K ratio of 57/43 (y = 0.07).

Shift of optical absorption edge in SnO2 films with high concentrations of nitrogen grown by chemical vapor deposition

The optical and electrical properties of n-type SnO2 films with high concentrations of nitrogen (SnO2:N) grown by chemical vapor deposition are studied. The carrier concentration increases from 4.1 × 1018 to 3.9 × 1019 cm−3 and the absorption edge shifts from 4.26 to 4.08 eV with increasing NH3 flow rate. Typical Urbach tails were observed from the absorption spectra and the Urbach energy increases from 0.321 to 0.526 eV with increasing NH3 flow rate. An “effective” absorption edge of about 4.61 eV was obtained for all investigated samples from fitting the extrapolations of the Urbach tails. Burstein-Moss effect, electron-impurity, and electron-electron interactions are shown to play a minor role for the shift of the absorption edges in SnO2:N thin films.

Single-phase quaternary MgxZn1−xO1−ySy alloy thin films grown by pulsed laser deposition

Quaternary-alloy MgxZn1−xO1−ySy thin films were grown quasi-epitaxially on c-plane sapphire substrates by pulsed laser deposition. Single-phase wurtzite MgxZn1−xO1−ySy films with compositions of 0.07 < x < 0.21 and y ≥ 0.8 were achieved using various ceramic targets. The S contents in the quaternary alloy films were far beyond the reported solid solubility limits of S in single-phase ternary alloy ZnO1−ySy films. The bandgap of MgxZn1−xO1−ySy, inferred from optical transmission measurements, was narrower than the bandgap of MgxZn1−xO while broadened compared with that of ZnO1−ySy. The broadening effect was enhanced with the increase of Mg content. The simultaneous substitution of cation (Zn2+) and anion (O2−) by isoelectronic elements (Mg2+ and S2−) offers further flexibility for the band-gap engineering and potentially facilitates the p-type doping of ZnO.

Energy storage characteristics of (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics with high Sn content

(Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectric (AFE) materials have been widely investigated for advanced pulsed power capacitors because of their fast charge-discharge rates and superior energy-storage capacity. For practical applications, pulsed power capacitors require not only large energy density but also high energy efficiency, which are very difficult to achieve simultaneously. To address this problem, we herein investigate the energy-storage properties of PLZST AFE ceramics with a high Sn content by considering that the introduction of Sn can make the polarization versus electric-field (P-E) hysteresis loops slimmer. The results show that an optimum Sn content leads to the realization of both large recoverable energy density (Wre) and high energy efficiency (η) in a single material. With a Sn content of 46%, the PLZST AFE ceramic exhibits the best room-temperature energy storage properties with a Wre value as large as 3.2 J/cm3 and an η value as high as 86.5%. In addition, both its Wre and η vary very slightly in the wide temperature range of 20–120 °C. The high Wre and η values and their good thermal stability make the Pb0.97La0.02(Zr0.50Sn0.46Ti0.04)O3 AFE ceramic a promising material for making pulsed power capacitors usable in various conditions.(Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectric (AFE) materials have been widely investigated for advanced pulsed power capacitors because of their fast charge-discharge rates and superior energy-storage capacity. For practical applications, pulsed power capacitors require not only large energy density but also high energy efficiency, which are very difficult to achieve simultaneously. To address this problem, we herein investigate the energy-storage properties of PLZST AFE ceramics with a high Sn content by considering that the introduction of Sn can make the polarization versus electric-field (P-E) hysteresis loops slimmer. The results show that an optimum Sn content leads to the realization of both large recoverable energy density (Wre) and high energy efficiency (η) in a single material. With a Sn content of 46%, the PLZST AFE ceramic exhibits the best room-temperature energy storage properties with a Wre value as large as 3.2 J/cm3 and an η value as high as 86.5%. In addition, both its Wre and η vary v...

Structural and optical properties of delafossite-type CuAlO 2 thin films prepared by RF reactive sputtering

Delafossite-type CuAlO 2 thin films have been deposited by radio frequency (RF) reactive sputtering on sapphire using a CuAlO 2 ceramic target. A study of structural and optical properties was performed on films of varying deposition parameters such as substrate temperature and oxygen partial pressure and also post annealing. The crystalline phase in the films was identified to be the delafossite structure by x-ray diffraction. The optical properties, such as the wavelength dependence of the transmittance and the band gap, were determined. The average transmittance is 80% in the wavelength range of 400-1500 nm and the band gap is 3.81 eV.