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Epitaxial (Bi, K)TiO3 films with 800- to 900-nm thicknesses were grown hydrothermally at 200 °C on SrTiO3 substrates covered with SrRuO3 layers. Perfectly (001)-oriented films grew on (100)SrTiO3 due to good lattice matching. Films on (110)SrTiO3 had mixed orientations of dominant (110) and minor (101), while three types of (111) orientations with in-plane 120° rotation were observed for the film on (111)SrTiO3. The (101) and (110) orientations of the film deposited on (110)SrTiO3 were tilted by approximately 2.6° and 1.6°, respectively, from surface normal due to the formation of a 90° domain with a twinning plane. The plane-view measurement for the film deposited on (111)SrTiO3 showed nine spots. These are explained by the presence of 15 possible spots resulting from the relaxed 90° domain combination and by overlapping. The lattice parameters of these films explain the tilting angles of these domains. These results reveal the formation of perfectly relaxed 90° domain structures for films grown on (110) and (111)SrTiO3. This differs from our previous data for tetragonal Pb(Zr,Ti)O3 films grown above TC on (110) and (111)SrTiO3 because the present films directly grow the ferroelectric films below TC without phase change. The tilting angle of the polar-axis and the volume fraction of the 90° domain can explain the piezoelectric responses of these films assuming that films have purely an up-state. This suggests that these films show almost pure up-state polarization without 180° domains, at least along surface-normal directions. These data show that these films have domain structures different from the well-known ones for the tetragonal Pb(Zr,Ti)O3 films. [ABSTRACT FROM AUTHOR]

The strain‐driven morphotropic boundary in BiFeO3 can enhance the piezoelectric properties. However, the tetragonal phase has generally been observed in BiFeO3 films grown on substrates with intense compressive strain (more than −4.5%) within a limited thickness range (<300 nm) due to significant thickness‐dependent strain relaxation during film growth at high deposition temperatures. This work proposes suppressing thickness‐dependent strain relaxation by decreasing growth temperature. Utilizing a hydrothermal method, the growth temperature of epitaxial BiFeO3 films decreases to 200 °C. As a result, the tetragonal phase is observed in 600‐nm‐thick BiFeO3 film on (001) SrTiO3 substrates (strain equals only −1.5%), accompanied by the monoclinic phase. This SrTiO3‐available morphotropic phase boundary significantly enhances the piezoelectric response (d33,f′=110pmV−1)$ {({d}^{\prime}_{\rm 33,f} = 110\, {\rm pm\, V}^{-1})} $ in epitaxial BiFeO3 film. Ex situ and in situ measurements, theoretical calculations, and simulation confirm that the SrTiO3‐available morphotropic phase boundary originates from the suppressed strain relaxation. Furthermore, a critical temperature (400 °C), below which the tetragonal phase can be maintained, is identified to offer an applicable strategy for extending strain‐driven morphotropic phase boundary for high‐performance piezoelectric films. [ABSTRACT FROM AUTHOR]

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The oriented lamellar K-rich exsolutions within clinopyroxene host were recognized in garnet peridotite massif at Zhimafang in the Sulu ultrahigh pressure metamorphic terrane, eastern China. EMP and TEM analyses revealed that the composition and the index of electron diffraction for this exsolution are corresponding with phlogopite, and the shape is the lamellae with 1 µm in width and 5 to 30 µm in length. Moreover, the topotaxy is that the (001) of K-rich exsolution parallels to (100) of the clinopyroxene host. The electron diffraction analyzing shows the exsolution is of a 1M polymorphism. The high-resolution lattice fringe image displays the stack features along [001], which only a layer mineral shows. We conclude that the clinopyroxene with 1M and K-rich exsolution was probably derived from mantle depths over 240 km, thus resulting from decompressional exsolution in the initial stage of slab exhumation. [ABSTRACT FROM AUTHOR]