[en] Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films have been successfully fabricated on p-type Si(100) substrates by a sol-gel spin-coating method. The microstructures and surface morphologies of the BLT thin films on p-type Si(100) substrates annealed at 700 deg. C for 30 min in oxygen atmosphere were examined by an X-ray diffractometer and a scanning electron microscope, respectively. The BLT/p-type Si(100) capacitors annealed at 700 deg. C for 30 min exhibit good capacitance-voltage (C-V) characteristics and large memory window of approximately 6 V with a sweep voltage of ±16 V. From the frequency dependency of C-V characteristics of the BLT/p-type Si(100) capacitors, the fixed charge density (N_fc) at the interface of BLT/p-type Si(100) was calculated as approximately 1.24x10¹²/cm². The humps and valleys observed in C-V curves were interpreted by introducing the electron charge injection and barrier-lowering effect at the interface of BLT/p-type Si(100). Based on the voltage and the frequency dependent C-V measurements, the memory windows of BLT/p-type Si(100) capacitor are significantly influenced by the electron charge injection and polarization reverse

[en] Lanthanum-doped bismuth titanate, Bi_3.25La_0.75Ti₃O₁₂ (BLT), thin films were grown on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol-gel spin coating process followed by annealing at 550-700 deg. C for crystallization of the thin films. From the X-ray diffraction (XRD) studies, it was found that the ratio of c-axis oriented grains in the annealed BLT thin films strongly depends on the annealing temperature. The remanent polarization (2P_r) and the coercive field (2E_c) values of the BLT thin film capacitor annealed at 650 deg. C for 30 min were approximately 70 μC/cm² and 132 kV/cm at electric field of 200 kV/cm, respectively. The current-voltage characteristics were found to be an Ohmic conduction at low voltage region and a space charge conduction at high voltage region. The dipole polarization and the leakage current of the BLT thin film capacitor were interpreted by introducing charge traps and charge injections. Also, the BLT thin film capacitor annealed at 650 deg. C exhibited a good fatigue endurance under bipolar pulse up to 4.5x10¹⁰ read/write cycles. From the results, the lanthanum-doped BIT thin film should be considered seriously for an environmentally safe lead-free ferroelectric material with an excellent ferroelectricity

[en] The effect of Ce3+-ion doping on the structural, electrical and ferroelectric properties of the Aurivillius K0.5Bi4.5Ti4O15 thin films are reported. For the purpose of this study, K0.5Bi4.5Ti4O15 and K0.5Bi4.0Ce0.5Ti4O15 thin films were deposited on Pt(111)/Ti/Si)₂/Si(100) substrates by using chemical solution deposition method. Formation of the Aurivillius structure was con-firmed through X-ray diffraction and Raman scattering studies. From the experimental results, tremendous improvements in the electrical and the ferroelectric properties were observed for the K0.5Bi4.0Ce0.5Ti4O15 thin film. The ferroelectric polarization-electric field (P-E) hysteresis loops study showed a largely enhanced remnant polarization (2Pr), with a value of 52.8 μC/cm2 for the K0.5Bi4.0Ce0.5Ti4O15 thin film measured at an applied electric field of 595 kV/cm. Furthermore, a low leakage current density value of 1.38 × 10−8 A/cm2 was measured at an applied electric field of 100 kV/cm for the K0.5Bi4.0Ce0.5Ti4O15 thin film.

[en] (Bi_0.95La_0.05)(Fe_0.97Cr_0.03)O₃/CoFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by using a chemical solution deposition method. By introducing CoFe₂O₄ buffer layer, the leakage current density and the multiferroic properties have been significantly improved. Low leakage current density of 3.3 × 10⁻⁷ A/cm² at 100 kV/cm, saturated ferroelectric hysteresis loop with 2P_r of 33 μC/cm² and 2E_c of 1120 kV/cm at applied electric field of 1180 kV/cm and ferromagnetic hysteresis loop with 2M_r of 39 kA/m and 2H_c of 298 kA/m at the magnetic field of 1587 kA/m were observed in the double layered thin film at room temperature. The improved electrical and multiferroic properties are ascribed to the stabilized perovskite structure by reducing oxygen vacancies due to the co-doping elements, which may also suppress the cycloid spin structure in BiFeO₃. Furthermore, CoFe₂O₄ buffer layer acts as a current barrier of (La, Cr) co-doped BiFeO₃. - Highlights: • Chemical solution deposition of (Bi_0.95La_0.05)(Fe_0.97Cr_0.03)O₃/CoFe₂O₄ double layered thin film. • Analysis of structural, electrical and magnetic properties. • Simultaneous ferroelectric and ferromagnetic properties were observed

[en] The influence of SrZrO3 (SZ) addition on the crystal structure, piezoelectric and the dielectric properties of lead-free Bi0.5Na0.5TiO3 (BNT−SZ100x, with x = 0 − 0.10) ceramics was systematically investigated. A significant reduction in the grain size was observed with SZ substitution. The X-ray diffraction analysis of the sintered BNT−SZ ceramics revealed a single perovskite phase with a pseudocubic symmetry; however, electric poling indicated a non-cubic distortion in the poled BNT−SZ ceramics. With increase in the SZ content, the temperature of maximum dielectric constant (Tm) shifted towards lower temperatures, and the curves became more diffuse. Enhanced piezoelectric constant (d33 = 102 pC/N) and polarization response were observed for the BNT−SZ5 ceramics. The results indicated that SZ substitution induced a transition from a ferroelectric to relaxor state with a field-induced strain of 0.24% for BNT−SZ9 corresponding to a normalized strain of 340 pm/V.

[en] Praseodymium-substituted bismuth titanate, Bi_3.4Pr_0.6Ti₃O₁₂ (BPT), thin films were successfully fabricated on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol-gel method. Fabricated BPT thin films were found to be random orientations, which were confirmed by X-ray diffraction experiment and scanning electron microscope analysis. The remanent polarization (2P _r) and the coercive field of the BPT thin film annealed at 650 deg. C were 62 μC/cm² and 205 kV/cm, respectively, at an applied electric field of 320 kV/cm. The measured 2P _r of the randomly oriented BPT thin film is larger than those of Bi_4-xLa _xTi₃O₁₂ (x=0.75) and Bi₄Ti₃O₁₂ thin films, and comparable with those of other lanthanide-substituted Bi₄Ti₃O₁₂ thin films. The BPT thin film exhibits a good fatigue resistance up to 1.5x10¹⁰ switching cycles at a frequency of 1 MHz with applied electric field of 120-240 kV/cm. These results indicate that the randomly oriented BPT thin film is a promising candidate among ferroelectric materials useful in lead-free nonvolatile ferroelectric random access memory applications

[en] Lead-free piezoelectric 0.97(Bi0.5Na0.5Ti1−xNbx)O3-0.03BaZrO3 (BNT-BZ3) ceramics (x = 0 ∼ 0.03) were prepared by a conventional solid-state reaction method. X-ray diffraction patterns revealed the formation of single-phase perovskite structure with x ≤ 0.015. The depolarization temperature and the dielectric constant decreased with increasing Nb content. The remanent polarization (Pr) and the piezoelectric constant (d33) increased from 28 μC/cm2 and 98 pC/N for x = 0 to 31 μC/cm2 and 128 pC/N for x = 0.005, respectively. In addition, the electric field induced strain was enhanced with a maximum value Smax = 0.17% with a normalized piezoelectric coefficient of d∗ 33 = 283 pm/V at an applied electric field of 6 kV/mm for x = 0.015.

[en] High-quality powders of Ba_0.6K_0.4BiO₃(BKBO) superconductors are synthesized by a new technique to prevent a potassium deficiency. The structures of BKBO are investigated using a high-resolution neutron-powder diffractometer in the the temperature range from 10 K to 310 K. Although the structure below the transition temperature, T_c, is theoretically expected to be a structural distortion (or tetragonal structure) due to the electron-phonon interaction, the cubic structure is observed experimentally. By analyzing oxygen vibrations of BiO₆ octahedra in BKBO with a Rietvelt refinement, we found that the vibrations of oxygen atoms decrease dramatically in a horizontal (or ab plane) direction rather than in a vertical (or c-axis) direction of the Bi-O plane when BKBO contracts with decreasing temperature. Anomalously large changes of the thermal parameters of oxygen atoms near T_c are obtained although a structural change is not observed. The volume of BKBO at 10 K is contracted by 0.7 % relative to that at 310 K. A remnant charge density-wave structure is observed in BKBO superconductors and is caused by an instability of the metal-insulator transition

[en] The effect of BaZrO₃ (BZ) addition on the crystal structure, ferroelectric, and piezoelectric properties of Na_0.5Bi_0.5TiO₃ (NBT) ceramics synthesized by a conventional solid-state reaction method was systemically investigated. The X-ray diffraction profile reveals the formation of single-phase perovskite structure for all BZ modified NBT ceramics in composition range (x = 0-0.08). With the increase in BZ content, the maximum dielectric constant (T_m) and depolarization temperature (T_d) peaks shift towards lower temperatures. At room temperature, the ferroelectric response increase with increase in BZ concentration. A maximum value of remanent polarization (P_r) 30 μC/cm² was obtained at x = 0.04 and, however, with further increase in BZ content polarizations values decrease. The piezoelectric constant (d₃₃) increased from 60 pC/N for pure NBT to 112 pC/N for x = 0.040. Furthermore, a significant enhancement in the normalized strain (d^*₃₃ = S_max/E_max = 500 pm/V) was observed at x = 0.055 which can be attributed to ferroelectric and relaxor ferroelectric phase transformation. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] The Bi_3.4Pr_0.6Ti₃O₁₂ (BPT) thin film and powder have been prepared by a sol-gel method by annealing at 700 .deg. C. Randomly oriented BPT thin film exhibits a large remanent polarization, 2P_r = 62 μC/cm². Structure of sol-gel derived BPT has been refined by a rietveld method resulting a reasonable goodness of fit (_wR_p = 6.9%, and R_p = 5.5%) using orthorhombic (B2cb, a = 5.4221 A , b = 5.4032 A , and c = 32.8361 A ). Two different TiO₆ octahedra exhibit different polarization directions; (100) from Ti(1)O₆, and close to (111) from Ti(2)O₆, which explains large 2P_r of the randomly oriented BPT thin film