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  1. Abstract Microstructural analysis of the BaZrO 3 (BZO)/YBa 2 Cu 3 O 7 (YBCO) interface has revealed a highly defective and oxygen deficient 2-3 nm thick YBCO column surrounding the BZO one-dimensional artificial pinning centers (1D-APCs). The resulting semi-coherent interface is the consequence of the ∼7.7% BZO/YBCO lattice mismatch and is responsible for the low pinning efficiency of BZO 1D-APCs. Herein, we report an interface engineering approach of dynamic Ca/Cu replacement on YBCO lattice to reduce/eliminate the BZO/YBCO lattice mismatch for improved pinning at a wide angular range of the magnetic field orientation. The Ca/Cu replacement induces a local elongation of the YBCO c-lattice near the BZO/YBCO interface, thereby ensuring a reduction in the BZO/YBCO lattice mismatch to ∼1.4% and a coherent BZO/YBCO interface. This has resulted in enhanced pinning at B//c-axis and a broad angular range of B-field orientation. For example, the 6 vol.% BZO/YBCO film with interface engineering exhibits F p ∼158 GN/m 3 at 65 K and B//c-axis, which is 440% higher than the ∼36.1 GN/m 3 for the reference 6% BZO/YBCO sample, and enhanced J c and F p in a wide angular range up to ∼ 80°. This result illustrates a facile scheme for engineeringmore »1D-APC/YBCO interface to resume the pristine pinning efficiency of the 1D-APCs.« less
    Free, publicly-accessible full text available May 1, 2023
  2. Abstract One-dimensional c -axis-aligned BaZrO 3 (BZO) nanorods are regarded as strong one-dimensional artificial pinning centers (1D-APCs) in BZO-doped YaBa 2 Cu 3 O 7− x (BZO/YBCO) nanocomposite films. However, a microstructure analysis has revealed a defective, oxygen-deficient YBCO column around the BZO 1D-APCs due to the large lattice mismatch of ∼7.7% between the BZO (3a = 1.26 nm) and YBCO (c = 1.17 nm), which has been blamed for the reduced pinning efficiency of BZO 1D-APCs. Herein, we report a dynamic lattice enlargement approach on the tensile strained YBCO lattice during the BZO 1D-APCs growth to induce c -axis elongation of the YBCO lattice up to 1.26 nm near the BZO 1D-APC/YBCO interface via Ca/Cu substitution on single Cu-O planes of YBCO, which prevents the interfacial defect formation by reducing the BZO/YBCO lattice mismatch to ∼1.4%. Specifically, this is achieved by inserting thin Ca 0.3 Y 0.7 Ba 2 Cu 3 O 7− x (CaY-123) spacers as the Ca reservoir in 2–6 vol.% BZO/YBCO nanocomposite multilayer (ML) films. A defect-free, coherent BZO 1D-APC/YBCO interface is confirmed in transmission electron microscopy and elemental distribution analyses. Excitingly, up to five-fold enhancement of J c ( B ) at magnetic field Bmore »= 9.0 T// c -axis and 65 K–77 K was obtained in the ML samples as compared to their BZO/YBCO single-layer (SL) counterpart’s. This has led to a record high pinning force density F p together with significantly enhanced B max at which F p reaches its maximum value F p,max for BZO 1D-APCs at B // c -axis. At 65 K, the F p,max ∼158 GN m −3 and B max ∼ 8.0 T for the 6% BZO/YBCO ML samples represent a significant enhancement over F p,max ∼ 36.1 GN m −3 and B max ∼ 5.0 T for the 6% BZO/YBCO SL counterparts. This result not only illustrates the critical importance of a coherent BZO 1D-APC/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO 1D-APCs.« less
  3. Sm-doped BiFeO 3 (Bi 0.85 Sm 0.15 FeO 3 , or BSFO) thin films were fabricated on (001) SrTiO 3 (STO) substrates by pulsed laser deposition (PLD) over a range of deposition temperatures (600 °C, 640 °C and 670 °C). Detailed analysis of their microstructure via X-ray diffraction (XRD) and transmission electron microscopy (TEM) shows the deposition temperature dependence of ferroelectric (FE) and antiferroelectric (AFE) phase formation in BSFO. The Sm dopants are clearly detected by high-resolution scanning transmission electron microscopy (HR-STEM) and prove effective in controlling the ferroelectric properties of BSFO. The BSFO ( T dep = 670 °C) presents larger remnant polarization (Pr) than the other two BSFO ( T dep = 600 °C, 640 °C) and pure BiFeO 3 (BFO) thin films. This study paves a simple way for enhancing the ferroelectric properties of BSFO via deposition temperature and further promoting BFO practical applications.
  4. A new two-phase BaTiO 3  : La 0.7 Sr 0.3 MnO 3 nanocomposite system with a molar ratio of 8 : 2 has been grown on single crystal SrTiO 3 (001) substrates using a one-step pulsed laser deposition technique. Vertically aligned nanocomposite thin films with ultra-thin La 0.7 Sr 0.3 MnO 3 pillars embedded in the BaTiO 3 matrix have been obtained and the geometry of the pillars varies with deposition frequency. The room temperature multiferroic properties, including ferromagnetism and ferroelectricity, have been demonstrated. Anisotropic ferromagnetism and dielectric constants have been observed, which can be tuned by deposition frequencies. The tunable anisotropic optical properties originated from the conducting pillars in the dielectric matrix structure, which cause different electron transport paths. In addition, tunable band gaps have been discovered in the nanocomposites. This multiferroic and anisotropic system has shown its great potentials towards multiferroics and non-linear optics.
  5. A phase transition material, VO 2 , with a semiconductor-to-metal transition (SMT) near 341 K (68 °C) has attracted significant research interest because of drastic changes in its electrical resistivity and optical dielectric properties. To address its application needs at specific temperatures, tunable SMT temperatures are highly desired. In this work, effective transition temperature ( T c ) tuning of VO 2 has been demonstrated via a novel Pt : VO 2 nanocomposite design, i.e. , uniform Pt nanoparticles (NPs) embedded in the VO 2 matrix. Interestingly, a bidirectional tuning has been achieved, i.e. , the transition temperature can be systematically tuned to as low as 329.16 K or as high as 360.74 K, with the average diameter of Pt NPs increasing from 1.56 to 4.26 nm. Optical properties, including transmittance ( T %) and dielectric permittivity ( ε ′) were all effectively tuned accordingly. All Pt : VO 2 nanocomposite thin films maintain reasonable SMT properties, i.e. sharp phase transition and narrow width of thermal hysteresis. The bidirectional T c tuning is attributed to two factors: the reconstruction of the band structure at the Pt : VO 2 interface and the change of the Pt : VO 2 phase boundary density. This demonstration sheds light on phasemore »transition tuning of VO 2 at both room temperature and high temperature, which provides a promising approach for VO 2 -based novel electronics and photonics operating under specific temperatures.« less
  6. Bi 3 MoM T O 9 (BMoM T O; M T , transition metals of Mn, Fe, Co and Ni) thin films with a layered supercell structure have been deposited on LaAlO 3 (001) substrates by pulsed laser deposition. Microstructural analysis suggests that pillar-like domains with higher transition metal concentration ( e.g. , Mn, Fe, Co and Ni) are embedded in the Mo-rich matrix with layered supercell structures. The layered supercell structure of the BMoM T O thin films accounts for the anisotropic multifunctionalities such as the magnetic easy axis along the in-plane direction, and the anisotropic optical properties. Ferroelectricity and ferromagnetism have been demonstrated in the thin films at room temperature, which confirms the multiferroic nature of the system. By varying the transition metal M T in the film, the band gaps of the BMoM T O films can be effectively tuned from 2.44 eV to 2.82 eV, while the out-of-plane dielectric constant of the thin films also varies. The newly discovered layered nanocomposite systems present their potential in ferroelectrics, multiferroics and non-linear optics.