g-Sao Chen

Polar nanoregions and dielectric properties in high-strain lead-free 0.93(Bi1/2Na1/2)TiO3-0.07BaTiO3 piezoelectric single crystals

A structural coexistence of rhombohedral (R) and tetragonal (T) phases has been revealed in the (001)c-cut lead-free 0.93(Bi1/2Na1/2)TiO3–0.07BaTiO3 (BNB7T) piezoelectric crystals, which grown by the self-flux method, in the lower temperatures by high-resolution synchrotron X-ray diffraction, reciprocal space mapping, and transmission electron microscopy. The dielectric permittivity exhibits a thermal hysteresis in the region of 120–260 °C, implying a first-order-like phase transition from R+T to T. The real part (e′) of dielectric permittivity begins to deviates from the Curie-Weiss equation, e′ = C/(T − To), from the Burns temperature TB = 460 °C, below which the polar nanoregions (or nanoclusters) develop and attenuate dielectric responses. The polar nanoregions of 5–10 nm were revealed by high-resolution transmission electron microscope. The normal piezoelectric coefficient d33 exhibits a rapid increase at E = 15–20 kV/cm and reaches a maximum of d33 ∼450 pC/N. The high piezoelectric response and E-fi...

Structural stability and depolarization of manganese-doped (Bi0.5Na0.5)1−xBaxTiO3 relaxor ferroelectrics

This work reveals that 0.5 mol. % manganese (Mn) doping in (Bi0.5Na0.5)1−xBaxTiO3 (x = 0 and 0.075) solid solutions can increase structural thermal stability, depolarization temperature (Td), piezoelectric coefficient (d33), and electromechanical coupling factor (kt). High-resolution X-ray diffraction and transmission electron microscopy reveal coexistence of rhombohedral (R) R3c and tetragonal (T) P4bm phases in (Bi0.5Na0.5)0.925Ba0.075TiO3 (BN7.5BT) and 0.5 mol. % Mn-doped BN7.5BT (BN7.5BT-0.5Mn). (Bi0.5Na0.5)TiO3 (BNT) and BN7.5BT show an R − R + T phase transition, which does not occur in 0.5 mol. % Mn-doped BNT (BNT-0.5Mn) and BN7.5BT-0.5Mn. Dielectric permittivity (e′) follows the Curie-Weiss equation, e′ = C/(T − To), above the Burns temperature (TB), below which polar nanoregions begin to develop. The direct piezoelectric coefficient (d33) and electromechanical coupling factor (kt) of BN7.5BT-0.5Mn reach 190 pC/N and 47%.

Measurement for temperature on a LED lamp

LED demonstrates a number of benefits compared to traditional incandescent lamps and fluorescent lamps. However, the thermal problem that is brought by heat generated within the LED itself is still a bottleneck that limits the stability, reliability and lifetime of high power LED. In order to understand the temperature characteristics of the LED lamp, this paper utilized the thermocouples to measure the temperature on LED lamp. The effects of the ambient temperature on the surface temperature of the LED lamp were presented.

Development of CaMgSi 2 O 6 diopside glass ceramic as microwave dielectric material

Development of a CaMgSi<inf>2</inf>O<inf>6</inf> diopside phase as a microwave dielectric material was attempted in the present work. A glass frit was made by mixing oxides of the MgO-CaO-2SiO<inf>2</inf>-ZrO<inf>2</inf> system, melted at 1500°C and then quenched. The glass frit was pulverized and pressed to discs. Controlled annealing at various temperatures was carried out to produce CaMgSi<inf>2</inf>O<inf>6</inf> diopside phase in the discs. The microstructural features, microwave dielectric properties and nucleating/growth mechanism of ZrO<inf>2</inf> added CaMgSi<inf>2</inf>O<inf>6</inf> are analyzed using scanning electron microscope (SEM), transmission electron microscopy (TEM) and impedance spectroscopy. Experimental results demonstrated that an amorphous phase MgO-CaO-2SiO<inf>2</inf> and m-ZrO<inf>2</inf> were forms after melted at 1500°C, and a glass-ceramic structure of CaMgSi<inf>2</inf>O<inf>6</inf> as well as a tetragonal zirconia (t-ZrO<inf>2</inf>) was precipitated from amorphous matrix after thermal treatment at 950°C. The diopside phase without addition m-ZrO<inf>2</inf> reveals only weak crystallization. It is found the crystallization enhancement of CaMgSi<inf>2</inf>O<inf>6</inf> specimen is significant due to heterogeneous nucleation. Quality factor of CaMgSi<inf>2</inf>O<inf>6</inf> was remakedly enhanced by adding ZrO<inf>2</inf> nucleating agent, indicating nucleation and growth control of the diopside phase plays a primary role in the CaMgSi<inf>2</inf>O<inf>6</inf> glass-ceramic system.

Microstructural evolution and electrical properties of base-metal electroded BaTi 4 O 9 materials with B-Si-Ba-Zn-O glass system

Barium titanate material systems are the basic microwave dielectrics attracting particular interests and subject to many researches due to lots of intriguing properties, such as, its high temperature stability, low loss, high dielectric constant etc. at microwave range. However, BaTi 4 O 9 and Ba 2 Ti 9 O 20 ceramics usually need very high sintering temperatures (∼1300°C and above) to achieve sufficient density. The present work attempts to investigate the microstructures and corresponding electric properties of low temperature co-fired BaTi 4 O 9 microwave dielectric ceramics with copper electrode and B-Si-Ba-Zn-O glass in reducing atmosphere. Experimental results show that specimens of BaTi 4 O 9 ceramics with various glass compositions and Cu-electrode exhibit different colors and can be attributed to glass diffusivity and reaction with Cu element during sintering. Glass composition plays an important role of the mass transportation of glass. B 2 O 3 /SiO 2 ratio determines glass viscosity and BaO/ZnO ratio contributes to wettability of glass with BaTi 4 O 9 ceramics. In x-ray diffraction patterns, we can observe different Ba-Ti-O phases with various Ba/Ti ratio. Ba 4 Ti 13 O 30 may form when the BaO content in glass is too high (BaO/ZnO ratio is greater than 2). Instead, the BaTi 6 O 13 appears as the content of BaO is low, such as BaO/ZnO ratio is smaller than 0.75. Both extreme conditions degrade the electrical properties of materials. Appropriate composition of glass not only improves material density during sintering, but also enhances phase stability of dielectrics and electrical properties.