Pengdi Han

Improved stability for piezoelectric crystals grown in the lead indium niobate–lead magnesium niobate–lead titanate system

Higher coercive fields (EC) and depoling temperatures (TR∕T) were obtained for crystals in the Pb(In1∕2Nb1∕2)O3–Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PIN–PMN–PT) ternary system. Data are given for a crystal boule with starting composition 0.24PIN-0.44PMN-0.32PT, and with chemical distributions along the growth direction. The dielectric, piezoelectric, and elastic properties were determined. Similar to binary PMN–PT, ternary PIN–PMN–PT crystals have outstanding piezoelectric properties (e.g., d33∼900–1900pm∕V, k33∼0.83–0.92). In addition, PIN stabilizes piezoelectric performance by doubling EC (∼6kV∕cm) and increasing TR∕T by ∼20°C. These improvements are advantageous for acoustic transducers used in high-drive applications.

In situ transmission electron microscopy study of electric-field-induced microcracking in single crystal Pb(Mg1/3Nb2/3)O3–PbTiO3

In this letter, we report in situ transmission electron microscopy (TEM) study of effect of a cyclic electric field on microcracking in a single crystal piezoelectric 0.66Pb(Mg1/3Nb2/3)O3–0.34PbTiO3. A TEM heating stage was modified to permit the in situ application of an electric field on the TEM sample surface. Microcrack initiation from a fine pore under an applied cyclic electric field was directly observed in the piezoelectric single crystal. Experimental procedures for in situ TEM studies were described.

Measurements Along the Growth Direction of PMN-PT Crystals: Dielectric, Piezoelectric, and Elastic Properties

Property measurements are reported for Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) single crystals grown along (001) by a seeded-melt method. Chemical segregation occurs during crystal growth, leading to property changes along the growth direction. Variations in dielectric, piezoelectric, and elastic properties were evaluated for specimens selected from the crystals. Room-temperature data are correlated with T_C and composition that ranged from 27 to 32% PT, i.e., in the vicinity of the morphotropic phase boundary (MPB). While there was little change in the high electromechanical coupling factor k₃₃ (0.87-0.92), both the piezoelectric charge coefficient d₃₃ (1100-1800 pC/N) and the free dielectric constant K₃₃ ^T (4400-7000) were found to vary significantly with position. Increases in d₃₃ and K₃₃ ^T were relatively offsetting in that the ratio yielded a relatively stable piezoelectric voltage coefficient g₃₃ (27-31 times 10^-3 Vm/N). Values are also reported for the elastic compliance (3.3-6.3 times 10^-11 m²/N) determined from resonance measurements. Enhancements in d₃₃ and K₃₃ ^T were associated with lattice softening (increasing s₃₃ ^E) as the composition approached the MPB. Details are reported for the piezoelectric, dielectric, and elastic properties as a function of growth direction, T_C, and composition. The results are useful for an understanding of properties in PMN-PT crystals and for the design of piezoelectric devices.

Development of the high-tc phase by recrystallization of melt-quenched BiCaSrCu oxides

Abstract Oxide materials in the Bi-Ca-Sr-Cu system were prepared by a melt-quench method. The starting compositions were 2-2-2-3, 2-3-2-4 and 2-4-2-5. Three superconducting phases, 2-0-2-1, 2-1-2-2 and 2-2-2-3, crystallized sequentially in specific heat-treatment regimes. The phases corresponded to the single-, double-, and triple-layered structures with T c values of 20, 80 and 105 K respectively. The high- T c phase developed after prolonged heat treatment at 865°C. Superconducting transitions as high as 105 K were observed. Our results suggest that an interaction between an unidentified liquid phase and 2-1-2-2 promotes the development of the 2-2-2-3 phase.

Growth and improved properties of ternary piezoelectric single crystals in lead indium niobate-lead magnesium niobate-lead titanate system

Ternary piezoelectric crystals Pb(In<inf>1/2</inf>Nb<inf>1/2</inf>)O<inf>3</inf>-Pb(Mg<inf>1/3</inf>Nb<inf>2/3</inf>)O<inf>3</inf>-PbTiO<inf>3</inf> (PIN-PMN-PT) have improved thermal and electrical stability than binary PMN-PT. To better understand crystal system and optimize crystal properties, we systematically investigated crystal growth for compositions between the two binary end-members, PMN-PT and PIN-PT. The ternary system has a compositional window where crystals can be grown directly from stoichiometric melt. PIN-PMN-PT crystals exhibited excellent piezoelectric properties (e.g., k<inf>33</inf> ∼0.87–0.92, d<inf>33</inf> ∼ 1000–2200 pm/V). Higher PIN content further stabilized piezoelectric performance by ∼ 40°C increase in T<inf>R/T</inf> and more than doubling E<inf>C</inf> (∼7.0 kV/cm). Such improvements are important for applications at elevated temperature and/or high-drive conditions.

Superconducting coatings in the system Bi-Ca-Sr-Cu-O prepared by plasma spraying

Superconducting coatings in the system Bi‐Ca‐Sr‐Cu‐O were deposited on alumina substrates by plasma spray methods. The coatings were superconducting in the ‘‘as‐sprayed’’ condition and improved with heat treatment. The best results were for coatings with resistivity values near 10 mΩ cm at room temperature and zero resistance at 96 K. The coatings had a magnetic transition near 80 K, with a weak diamagnetic signal up to 112 K. Superconductivity in the coatings was associated with two distinct phases, one of which was not identified. Scanning electron microscopy, x‐ray diffraction, electrical resistivity, and magnetic measurements were used to characterize the coatings.

Growth twins in Bi 2 Ca 1 Sr 2 Cu 2 O 8 superconductor single crystals

Large-scale twin structures in single crystal Bi{sub 2}Ca{sub 1}Sr{sub 2}Cu{sub 2}O{sub 8}(2122) are reported for the first time. Symmetrical 90{degree} (i.e., {ital a}-{ital b}) twins with a (110) type twin boundary were observed. A characteristic layer-growth morphology and jagged twin walls suggests that twin formation occurred layer by layer during crystal growth, i.e., the twins were growth twins. Hot-stage optical microscopy, x-ray diffraction, and electron microscopy results are discussed with reference to twin morphology.

Growth twins in Bi sub 2 Ca sub 1 Sr sub 2 Cu sub 2 O sub 8 superconductor single crystals

Large-scale twin structures in single crystal Bi{sub 2}Ca{sub 1}Sr{sub 2}Cu{sub 2}O{sub 8}(2122) are reported for the first time. Symmetrical 90{degree} (i.e., {ital a}-{ital b}) twins with a (110) type twin boundary were observed. A characteristic layer-growth morphology and jagged twin walls suggests that twin formation occurred layer by layer during crystal growth, i.e., the twins were growth twins. Hot-stage optical microscopy, x-ray diffraction, and electron microscopy results are discussed with reference to twin morphology.

Thermal processing of ceramic superconductors in the system Bi-Ca-Sr-Cu-O

Superconductors in the system Bi-Ca-Sr-Cu-O were prepared from mixtures with initial cation proportions of 1111 and 6356. The effects of heat-treatment conditions, particularly, temperature, atmosphere, and cooling rates, on diamagnetic transition characteristics, were investigated. Calcined powders were found to be comprised primarily of the “2122 phase”. The transition temperature associated with this phase was determined to range from 60–80 K, depending upon the thermal processing conditions. By contrast with YBa2Cu3O7−gd, the superconducting transition temperature, TC, was found to 1. (i) decrease on annealing in oxygen and 2. (ii) increase with increasing cooling rate in air. The increase in TC observed for rapid cooling and quenching was related to an oxygen deficiency effect rather than to the cooling rate per se. An additional phase associated with a higher transition temperature of 112 K was present in all samples. The Meissner effect for this secondary phase was greatest for powder calcined at temperatures lower than the optimum conditions for the formation of the 2122 phase. The Tc for the second phase was found to be independent of the thermal processing conditions.

Electrochemical synthesis of single-crystal (Ba0.05K0.95)BiO3·1/6H2O with the KSbO3 structure

A new compound with a cubic structure, (Ba{sub 0.05}K{sub 0.95})BiO{sub 3}{center_dot}1/6H{sub 2}O (BKBO), was synthesized by electrochemical crystal growth using a rotating anode in molten KOH flux at 255 C. The BKBO crystal had the KSbO{sub 3} structure and belonged to space group Im{bar 3} (No 204) with Z = 12. Refinement of X-ray diffraction data at room temperature gave a = 10.0204(2) {angstrom}, V = 1006.1(1) {angstrom}{sup 3}, and R = 2.4% for 1465 unique reflections. Potassium, barium, and hydrated oxygen were found to occupy different sites in the tunnel structure. The electrical conductivity at room temperature was similar to the ionic conductor KBiO{sub 3}. BKBO decomposed to Bi{sub 2}O{sub 3}, K{sub 2}O, and BaO above 400 C.