The crystal structures and dielectric, polarization, and piezoelectric properties of high-density x(Bi0.5K0.5)TiO3–(1−x)BiFeO3 ceramics were investigated. The results obtained using x-ray and neutron powder diffractions and transmission electron microscopy showed that a morphotropic phase boundary between the rhombohedral (ferroelectric) and pseudocubic (ferroelectric) phases is present in 0.4<x<0.43. Ceramics with x=0.4 exhibited a large remanent polarization of 52 μC/cm2 at 25 °C and their piezoelectric properties were maintained up to 300 °C. It is suggested that the presence of nanosized domains with a polar rhombohedral structure observed for x=0.4 is the origin of relaxor-like dielectric properties.

A giant electric-field-induced strain of 0.87% is reported for tetragonal (Bi0.5Na0.5)TiO3-(Bi0.5K0.5)TiO3-BaTiO3 single crystals along the [100]cubic direction, which is six times as large as that of Pb(Zr0.52Ti0.48)O3 ceramics. In situ x-ray diffraction measurements and transmission electron microscope observations show that the giant strain mainly originates from switching of nanosized 90° domains. Strain measurements indicate that the strain caused by the 90° domain switching is reversible for both unipolar and bipolar electric-field applications. The reversibility of the 90° domain switching can be explained by the interaction between the spontaneous polarization and the defect dipole composed of A-site vacancy and oxygen vacancy.

High-P O2 (oxygen pressure) crystal growth is developed for Bi 0:5 Na 0:5 TiO 3 single crystals based on defect chemistry at high temperatures. Thermogravimetric analysis shows that the vacancy formations of Bi and O at high temperatures are controlled by the surface reaction (oxygen desorption), which is suppressed at a higher P O2 . Bi 0:5 Na 0:5 TiO 3 crystals grown at a P O2 of 1 MPa exhibit a saturated remanent polarization of 44 mC/cm 2 along [110] cubic , suggesting a spontaneous polarization of 54 mC/cm 2 along [111] cubic (polar direction) of rhombohedral Bi 0:5 Na 0:5 TiO 3 . High-P O2 heat treatments are proposed to be effective for fabricating high-quality and high-performance ferroelectric/piezoelectric devices using Bi-based ferroelectric oxides.

1-4 However, the significant drop in the dielectric constant with decreased film thickness, widely known as "size effect," has been reported to become serious. [1][2][3][4] The size effect in thin film dielectrics has made it difficult to design their performance characteristics. There has therefore been a strong motivation to discover size-effect-free highly insulating dielectric materials with a high dielectric constant. In this letter, we propose thin films with c-axis-oriented bismuth layer-structured dielectrics ͑BLDs͒ as candidates for size-effect-free materials.BLDs have a natural superlattice structure along the c axis consisting of two kinds of two-dimensional nanolayers, i.e., a bismuth oxide ͑Bi 2 O 2 ͒ 2+ sheet and a pseudoperovskite block generally described as ͑A m−1 B m O 3m+1 ͒ 2− , where m is the number of BO 6 octahedra in a pseudoperovskite block. Interestingly, BLDs with even m exhibit no ferroelectricity along the c axis. 5,6 In our previous study, we found that c-axis-oriented epitaxial SrBi 2 Ta 2 O 9 ͑SBT, m =2͒ films exhibited no degradation in dielectric constant down to 20 nm in thickness, corresponding to eight unit cells.7 However, their dielectric constant of 55 was obviously not enough to replace the conventional perovskite-structured oxides. We therefore expanded our concept to a higher m of 4, i.e., SrBi 4 Ti 4 O 15 ͑SBTi͒ and CaBi 4 Ti 4 O 15 ͑CBTi͒, to obtain higher dielectric constant and to deepen the understanding of the basic characteristics of c-axis-oriented BLD films. As a result, we found the design concept of their properties and revealed that thin films of c-axis-oriented BLDs are promising candidates for high-density capacitor application. c-axis-oriented epitaxial SBTi and CBTi films were grown at a substrate temperature of 700°C by metal organic chemical vapor deposition. ͑001͒ c -oriented epitaxial SrRuO 3 ͑SRO͒ films having an atomically flat surface grown on ͑001͒STO single crystals were used as substrates. 8 The constituent phase and the orientation were identified by conventional x-ray diffraction ͑XRD͒. The crystal structure was analyzed in detail by XRD using synchrotron radiation ͑SPring-8, BL13XU͒. 9 The dielectric and insulation properties of the films were measured after formation of the top electrodes of 100 m Pt on the film surface followed by postannealing in an electrical furnace at 400°C for 30 min under 1 atm flowing oxygen ambience.a͒ Electronic

We have investigated the effects of high-oxygen-pressure crystal growth of ferroelectric Bi4Ti3O12 on the polarization properties along the a(b) axis. Domain observations by piezoresponse force microscope demonstrate that a small remanent polarization (Pr) for the crystals grown at 0.02MPa is attributed to the clamping of 90° domain walls by oxygen vacancies. The vacancy formation of Bi and O during crystal growth at high temperatures is suppressed at a higher oxygen pressure, leading to a larger Pr of 47μC∕cm2 for the crystals grown at 1MPa oxygen. High-oxygen-pressure sintering is proposed to be effective for obtaining Bi4Ti3O12-based devices with enhanced polarization properties.

Polyimide (PI)-based composites containing single-wall carbon nanohorn aggregate (NH) were fabricated using the spark plasma sintering (SPS) process. For comparison, composites with carbon nanotube (NT) and traditional graphite (Gr) were also fabricated. The NH was produced using CO 2 laser vaporization and a graphite target and the NT was produced by a chemical synthesis method. We evaluated the friction and wear properties of the PI-based composites with a reciprocating friction tester in air using an AISI 304 mating ball. NH drastically decreased the wear of PI-based composites; the specific wear rate of composite with NH of only 5 wt% was of the order of 10 )8 mm 3 /Nm, which was two orders of magnitude less than that of PI alone. The wear reduction ability of NT seemed to be slightly inferior to that of NH, although it was considerably better than that of Gr. NH and NT lowered the friction of composites. The friction coefficient of composite with 10 wt% NH was less than 0.25, although it was slightly higher than that of composite with 10 wt% Gr. There was no clear difference in the friction reduction effect of NH and NT. The further addition of Gr to composites with NH or NT rather deteriorated the antiwear property of composites, although the friction coefficient was slightly reduced. The transferred materials existed on the friction surface of the mating ball, sliding against composites with three types of carbon filler. These transferred materials seemed to correlate with the low friction and wear properties of composites.

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