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A BiFeO3 (BFO) film is epitaxially grown on an (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) substrate to investigate the lattice mismatch effect on the domain structure and lattice strain status within the BFO film. Atomic resolution scanning transmission electron microscope image, selected area electron diffraction (SAED) patterns, and X-ray reciprocal space mapping (XRSM) data clearly reveal that the lattice strain originating from the lattice mismatch between BFO and LSAT is relaxed by causing misfit dislocations in the BFO film. The SAED and XRSM data indicate that the crystal structure of BFO film is rhombohedral with the space group R3c. In particular, XRSM data acquired along two different in-plane orientations reveal that the BFO layer consists of two different domains that were 90° off each other with respect to the surface normal orientation. An atomistic model based on the crystal orientation relation found by SAED and XRSM shows that (1) the ferroelectric polarization axes of both domains are 35.6° with respect to the BFO film surface and (2) the two domains are consistent with the so-called 71° (and/or 109°) ferroelectric domains reported previously. The lattice mismatch of ∼2.8% calculated based on the epitaxial relation is proposed to be too large to be stored as elastic strain energy within the BFO layer. [ABSTRACT FROM AUTHOR]

Due to epitaxial strain, epitaxial thin films exhibit unique properties compared with those in bulk. However, the presence of defects within these films disrupts the strain-induced effects. Although high-temperature annealing is a promising way to improve film quality, high temperature weakens bottom electrode materials. To assess epitaxial strain's effects on the mitigation of other factors, there is a need for a novel bottom electrode material that can withstand high temperatures. In this study, we focused on Nb-doped CaMnO3 (CMNO) as a bottom electrode for the evaluation of BaTiO3 ferroelectricity. The CMNO epitaxial film was deposited on (100)SrTiO3 and showed electrical conductivity even after 1100 °C annealing. The ferroelectric material BaTiO3 was also epitaxially grown on CMNO/(100)SrTiO3 substrate, and its ferroelectric properties were evaluated. Finally, we revealed the ability of CMNO/(100)SrTiO3 to withstand temperatures up to 1100 °C as well as the notable enhancement of ferroelectric properties in the BaTiO3 film. [ABSTRACT FROM AUTHOR]

In this study, the ferroelectric phase of PbTiO3 (PTO) thin films was grown on cubic single-crystal KTaO3 (KTO) substrates using metal–organic chemical vapor deposition. X-ray diffraction (XRD) was used to reveal an a1/a2 domain structure, which remained unchanged down to a film thickness of 2 nm. The a1 and a2 polydomains do not have a simple tetragonal symmetry because aa∥ and aa⊥ do not have the same values. The crystallographic tilt angle, α, is defined based on the rotation angle of the PTO lattice with respect to the cubic phase of KTO substrates. The in-plane tetragonal distortion (ca∥/aa∥) and α decreased with the decrease in the film thickness, following the in-plane tetragonal geometric equation: α = tan − 1 ( c a ∥ a a ∥ ) − 45 ° . The isotropic tensile strains induced in-plane polarization directions along the [100] and [010] axes of the substrates. These axes are formed via the a1/a2 polydomain of the tetragonal-like phase. Moreover, synchrotron in-plane grazing incidence XRD and piezoelectric force microscopy were used to reveal the thickness dependency of the periodic domain width of the ferroelastic a1/a2 domain. The periodic domain width in the PTO films decreased, following Kittel's law, with the reduction in the film thickness. [ABSTRACT FROM AUTHOR]

GaFeO3-type oxides are promising multiferroic materials due to the coexistence of spontaneous magnetization and ferroelectric polarization properties at room temperature. As these ferroic properties feature a large anisotropy, single crystals are required. However, the magnetization of GaFeO3-type single crystals remains low at room temperature. In this study, we largely enhanced the magnetization at room temperature of GaFeO3-type single crystals by increasing the Fe content and co-doping Sc3+ and Al3+. Single crystals of AlxSc0.1−xGa0.6Fe1.3O3 (x = 0.01–0.04) were prepared using the optical floating-zone method. The single crystals were rod-shaped, with a diameter and length of ∼6 mm and 7 cm, respectively. X-ray diffraction measurements confirmed the ferroelectric polarization of the crystals. In addition, they exhibited room-temperature ferrimagnetism, with Curie temperature in the range of 326–338 K; the crystals exhibit magnetic anisotropy along the a-axis. The magnetization of the single crystal at 300 K and 0.3 kOe was 13 emu g−1, which is over ten times larger than those of previously reported single crystals with GaFeO3-type crystal structure. [ABSTRACT FROM AUTHOR]

The phase stability, ferroelectricity, and magnetism of highly crystalline epitaxial ε-Fe2O3 films deposited on SrTiO3(111) substrates are reported. Temperature-dependent x-ray diffraction measurements revealed that α-Fe2O3 appeared as a secondary phase after samples were annealed up to 1000 °C. A clear saturated and opened polarization–electric field hysteresis loop with the remnant polarization ∼2.6 μC cm−2 and coercive electric field ∼100 kV cm−1 was obtained at room temperature using a conventional ferroelectric measurement technique. The magnetic phase transition was observed at 155 K. Magnetization–magnetic field measurements revealed that magnetic softening via the phase transition accompanied a reduction in the coercive field from 10 to 6.8 kOe, which is smaller than the coercive field reduction previously observed for ε-Fe2O3 nanoparticles. [ABSTRACT FROM AUTHOR]

Domain structures of epitaxial PbTiO3 films grown on (100)cSrRuO3//(100)SrTiO3 substrates by metalorganic chemical vapor deposition were investigated by x-ray diffraction (XRD) and piezoresponse force microscopy (PFM) techniques. It was found that with increasing film thickness, the domain structure changed from simple (001) polarization orientation to a complicated mixture of (001) and (100) orientations. PFM mappings showed that in the thicker films (∼1100 nm), the zigzag (001)/(100) domain boundaries made an angle of approximately 87° instead of 90° typically observed in (001)/(100) domain patterns in thinner (<300 nm) films. Full-relaxed tilting angle θ1 + θ2 + θ3 = 3.4° obtained from cross-sectional profile analysis of topological step-terrace structure was in good agreement with 3.4° and 3.6° angle values obtained from XRD measurements and theoretical prediction, respectively. [ABSTRACT FROM AUTHOR]

Epitaxial (1-x)BaTiO3-xBi(Mg0.5Ti0.5)O3 films with x = 0 - 0.9 were grown on (111)cSrRuO3//(111)SrTiO3 substrates by pulsed laser deposition (PLD). Plotting the temperature where dielectric constant reaches a maximum {T[&eh;r(max.)]} versus Bi(Mg0.5,Ti0.5)O3 content present minimum at x = 0.1. On the other hand, the remanent polarization (Pr) and the effective transverse piezoelectric constant [d33(eff.)] showed minimum at 0.1 and 0.2, respectively, but increased with the increase of x in (1-x)BaTiO3-xBi(Mg0.5Ti0.5)O3 above these values. These results show the simultaneous increase of T[&eh;r(max.)] and d33(eff.) for the films above x = 0.2 that normally showed treads off characteristics. [ABSTRACT FROM AUTHOR]

xBiCoO3–(1-x)BiFeO3 films were deposited by metalorganic chemical vapor deposition. Although the film composition changed with deposition temperature, the composition could be adjusted by varying the input source gas composition at 700 °C. Moreover, adjusting the deposition time could change 0.16BiCoO3–0.84BiFeO3 film thickness. The crystal symmetry changed from rhombohedral to tetragonal as the film thickness decreased for 0.16BiCoO3–0.84BiFeO3 films grown on both (100)SrTiO3 and (100)cSrRuO3∥(100)SrTiO3 substrates, implying that the x value of the crystal symmetry boundaries between the tetragonal and rhombohedral structures changes with film thickness. [ABSTRACT FROM AUTHOR]

Both the ferroelectric and magnetic properties of polycrystalline BiFeO3 films fabricated by chemical solution deposition were enhanced by adding small amounts of cobalt. Addition of 3 at. % cobalt to BiFeO3 films increased the remanent polarization from 49 to 72 μC/cm2 and decreased the electric coercive field from 0.54 to 0.44 MV/cm. The ferroelectricity degraded when the cobalt concentration exceeded 9 at. % due to the formation of the secondary phases of Bi2Pt. The saturation magnetization was drastically enhanced by the addition of cobalt up to 12 at. %. This is because the magnetic moments are not canceled locally since the differences of magnetic moment between B-sites. The saturation magnetization decreased when the cobalt content exceeded 15 at. %, thereby attributing to the formation of a nonmagnetic secondary phase of Bi2Pt. It is concluded that both ferroelectric and magnetic properties were enhanced, provided only small amount of cobalt were added to the films. [ABSTRACT FROM AUTHOR]

To control the properties of multiferroic materials, substitution of magnetic elements is a useful technique. In this study, we fabricated GaCrxFe1−xO3 and Ga1−yCryFeO3 films by substituting Cr3+ (3d3) ions in GaFeO3 for magnetic Fe3+ (3d5) and nonmagnetic Ga3+ (d10) sites, respectively. The effect of the Cr substitution on the magnetic and dielectric properties was systematically investigated. The obtained GaCrxFe1−xO3 and Ga1−yCryFeO3 films (x ≤ 1/4 and y ≤ 1/2) simultaneously exhibit ferrimagnetism and ferroelectricity. For the GaCrxFe1−xO3 films, the magnetic transition temperature (TC) and magnetic anisotropy decrease with increasing x. On the other hand, for the Ga1−yCryFeO3 films, TC increases with increasing y. Unlike the GaFeO3 film, the Cr-substituted GFO films show a peak in the magnetization versus temperature curves and exhibit a sudden decrease in the coercive field near the peak, probably due to the formation of Fe3+–O–Cr3+ coupling which prefers to form ferromagnetic interactions in the antiferromagnetic Fe3+–O–Fe3+ networks. Furthermore, we found that the Cr-substituted GaFeO3 films show out-of-plane ferroelectricity at room temperature. [ABSTRACT FROM AUTHOR]

The structural and ferroelectric domain variants of highly strained BiFeO3 films grown on vicinal LaSrAlO4 substrates were studied by piezoelectric force microscopy and high-resolution x-ray reciprocal space mapping. Through symmetry breaking of the substrate surface, ferroelastic domain variants in the highly strained MC phase BiFeO3 can be greatly reduced in thinner, purely tetragonal-like films. More interestingly, in thicker, mixed phase films, the structural variants can also be tailored by substrate vicinality. These findings lead to better understanding of the phase evolution and polarization rotation process in the strain-driven polymorphic phase system. [ABSTRACT FROM AUTHOR]

Temperature and electric field dependencies of the dielectric and insulating properties of (001)-oriented epitaxial CaBi4Ti4O15 films grown on (100)cSrRuO3//(100)SrTiO3 substrates were investigated and compared with those of conventional (100)-oriented epitaxial (Ba0.3Sr0.7)TiO3 and SrTiO3 films. All films showed negative temperature dependency of the capacitance from 25 to 500 °C, and their changes were -18%, -83%, and -58% for CaBi4Ti4O15, (Ba0.3Sr0.7)TiO3, and SrTiO3 films, respectively. Smaller change of the capacitance against dc electric field was also observed for CaBi4Ti4O15 films. Moreover, the maximum leakage current density of CaBi4Ti4O15 films measured at ±100 kV/cm was below 10-3 A/cm2 up to 500 °C, which was smaller than those of (Ba0.3Sr0.7)TiO3 and SrTiO3 films. These results indicate that (001)-oriented CaBi4Ti4O15 films are a useful candidate as the capacitor material applicable for the high temperature use because of its high stability against temperature and an electric field as well as the good insulating characteristics. [ABSTRACT FROM AUTHOR]

(100)/(001)-oriented epitaxial PbTiO3 films thicker than 1 μm were grown on various types of substrates by chemical vapor deposition. The domain structures of these films with different volume fractions of (001) were investigated. Domain structures, consisting of (100)/(001)-oriented domains, were observed regardless of the type of substrate. However, the tilting angles of the a- and c-domains from the surface normal linearly changed with the volume fraction of the (001) orientation. These results suggest that the volume fraction of the (001) orientation is crucial in identifying the domain structure of PbTiO3 thick films. [ABSTRACT FROM AUTHOR]

Thin films of Bi(Fe1-xScx)O3 (BFSO) system were fabricated on (111)Pt/TiO2/SiO2/(100)Si substrates by chemical solution deposition to improve the electrical resistivity by substituting electrically unstable Fe3+ cations for stable Sc3+ cations. A single phase of perovskite was obtained in the range of x=0–0.30, in which selective replacement of Fe3+ and Sc3+ was confirmed in x=0–0.15 by using Raman measurement. The leakage current density of the BFSO films was reduced by increasing x. A well-saturated polarization–electric field hysteresis loop was obtained for BFSO films with x=0.15, showing remanent polarization of approximately 35 μC/cm2. [ABSTRACT FROM AUTHOR]

The xBiCoO3-(1-x)BiFeO3 [0 ≤ x ≤ 58 at. %] solid solution films were epitaxially grown on SrTiO3 (100) substrates, and the dependence of the magnetic properties on the BiCoO3 concentration was systematically investigated. The remanent magnetization (Mr) and coercive field (Hc) increased with the BiCoO3 in the case of rhombohedral composition (x ≤ 18 at. %), and it maximally enhanced at morphotropic phase boundary (MPB) (20 ≤ x ≤ 25 at. %). The magnetization decreased in the case of a tetragonal structure (30 at. % ≤ x). The magnetoelectric (ME) effect at room temperature expect to observe for the BiCoO3-BiFeO3 solid solution films in the case of the rhombohedral structure and for MPB. [ABSTRACT FROM AUTHOR]

Epitaxial films of tetragonal (001)/(100)-oriented (2/3)Bi(Zn1/2Ti1/2)O3-(1/3)BiFeO3 were grown on (100)cSrRuO3//(100)SrTiO3 substrates by metalorganic chemical vapor deposition. 93% of the film is occupied by c-domain [(001) orientation], and the out-of-plane (c-axis) and in-plane (a-axis) lattice parameters are 0.465 nm and 0.381 nm, respectively. The tetragonal distortion, (c/a)-1, is 22% which is 3.5 times larger than that of PbTiO3 (6.3%). High-angle annular dark-field-scanning transmission electron microscopy images show clear c-/a-domain structures with unusual boundary angles of 51°/39° due to the large c/a ratio of tetragonal phase. High temperature X-ray diffraction measurements reveal that the Curie temperature of this film is above 800 °C. [ABSTRACT FROM AUTHOR]