Xiaoping Li - Academia.edu (original) (raw)
Papers by Xiaoping Li
IEEE Journal of Photovoltaics
In-situ Cd-saturated growth of polycrystalline CdTe:As thin film was performed by metal organic c... more In-situ Cd-saturated growth of polycrystalline CdTe:As thin film was performed by metal organic chemical vapour deposition at a low temperature of 350°C, to investigate the impact on As doping and device V OC. Device characterization showed conversion efficiency of ∼14%, and V OC of 772 mV, which is an improvement to the baseline device with CdTe:As absorber layer grown at 390°C under non-saturated conditions. When the low temperature Cd-saturated growth was combined with chlorine heat treatment at a higher temperature of 440°C (in contrast with the standard 420°C) for 10 min, device efficiency improved to ∼17% with a high V OC of 877 mV. As a result, ∼100 mV boost in V OC from baseline is demonstrated with Cd-saturated CdTe:As device. Micro-photoluminescence and time-resolved photoluminescence measurements performed on these Cd-saturated CdTe:As devices confirmed that minority carrier lifetime significantly improved.
2022 IEEE 49th Photovoltaics Specialists Conference (PVSC)
In-situ Cd-saturated growth of polycrystalline CdTe:As thin film was performed by metal organic c... more In-situ Cd-saturated growth of polycrystalline CdTe:As thin film was performed by metal organic chemical vapour deposition at a low temperature of 350°C, to investigate the impact on As doping and device V OC. Device characterization showed conversion efficiency of ∼14%, and V OC of 772 mV, which is an improvement to the baseline device with CdTe:As absorber layer grown at 390°C under non-saturated conditions. When the low temperature Cd-saturated growth was combined with chlorine heat treatment at a higher temperature of 440°C (in contrast with the standard 420°C) for 10 min, device efficiency improved to ∼17% with a high V OC of 877 mV. As a result, ∼100 mV boost in V OC from baseline is demonstrated with Cd-saturated CdTe:As device. Micro-photoluminescence and time-resolved photoluminescence measurements performed on these Cd-saturated CdTe:As devices confirmed that minority carrier lifetime significantly improved.
Superconductor Science and Technology, 2006
We report on the thickness dependence of the superconducting characteristics including critical c... more We report on the thickness dependence of the superconducting characteristics including critical current I c , critical current density J c , transition temperature T c , irreversibility field H irr , bulk pinning force plot F p (H), and the normal state resistivity curve ρ(T) measured after successive ion milling of ~ 1 µm thick high I c YBa 2 Cu 3 O 7-x films made by an ex situ metal-organic deposition process on Ni-W rolling-assisted biaxially textured substrates (RABiTS TM). Contrary to many recent data, mostly on in situ pulsed laser deposition (PLD) films, which show strong depression of J c with increasing film thickness t, our films exhibit only a weak dependence of J c on t. The two better textured samples had full cross-section average J c,avg (77K,0T) ~ 4 MA/cm 2 near the buffer layer interface and ~3 MA/cm 2 at full thickness, despite significant current blocking due to ~30% porosity in the film. Taking account of the thickness dependence of the porosity, we estimate that the local, vortex-pinning current density is essentially independent of thickness, while accounting for the additional current-blocking effects of grain boundaries leads to local, vortex-pinning J c values well above 5 MA/cm 2. Such high local J c values are produced by strong three-dimensional vortex pinning which subdivides vortex lines into weakly coupled segments much shorter than the film thickness.
Microscopy and Microanalysis, 2010
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, ... more Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.
Journal of Physics: Conference Series, 2014
AMSC produces Second Generation (2G) HTS wire for utility power applications as well as coil, mot... more AMSC produces Second Generation (2G) HTS wire for utility power applications as well as coil, motor and generator solutions. In this paper, various types of AMSC's Amperium ® wire suitable to power cables, fault current limiters and coils are reviewed. In addition, recently developed performance-improvements in amperage, reduced ac power loss and mechanical properties are summarized. The introduction of thicker HTS layers coupled with optimized heat treatments to enhance critical current density dramatically improve both cable and coil wire current-carrying capability. A non-magnetic RABiTS TM substrate has now been developed to the point where it is compatible with the manufacturing process and capable of sustaining large critical currents. Finally, the ability of Amperium ® wires to withstand cable-winding stresses, and to exhibit the high transverse c-axis strength critical to the reliability of the wire in coils, are discussed.
Journal of Materials Research, 2005
Chemical solution processing of Gd2Zr2O7 (GZO) thin films via sol-gel and metalorganic decomposit... more Chemical solution processing of Gd2Zr2O7 (GZO) thin films via sol-gel and metalorganic decomposition (MOD) precursor routes have been studied on textured Ni-based tape substrates. Even though films processed by both techniques showed similar property characteristics, the MOD-derived samples developed a high degree of texture alignment at significantly lower temperatures. Both precursor chemistries resulted in exceptionally dense, pore-free, and smooth microstructures, reflected in the cross-sectional and plan-view high-resolution scanning and transmission electron microscopy studies. On the MOD GZO buffered Ni–3at.% W (Ni–W) substrates with additional CeO2/YSZ sputtered over layers, a 0.8-μm-thick YBa2Cu3O7−δ (YBCO) film, grown by an ex situ metalorganic trifluoroacetate precursor method, yielded critical current, Ic (77 K, self-field), of 100 A/cm width. Furthermore, using pulsed-laser deposited YBCO films, a zero-field superconducting critical current density, Jc (77 K), of 1 × 10...
Applied Physics Letters, 2007
The authors find the critical current anisotropy of a bilayer YBa2Cu3O7−δ film with different pin... more The authors find the critical current anisotropy of a bilayer YBa2Cu3O7−δ film with different pinning structures in each layer is the sum of the anisotropy of the two individual layers, revealing that it is possible to tune the anisotropy of the composite through variation of an individual layer’s thickness and pinning structure. YBa2Cu4Ox intergrowths and Dy2O3 nanodots were the dominant pinning structures in the top and bottom layers, respectively. The bottom layer of the composite was isolated using traditional Ar+ ion milling and the top layer was isolated using a focused ion beam, allowing each layer to be studied independently.
Applied Physics Letters, 2013
The in-field critical current of commercial YBa2Cu3O7 coated conductors can be substantially enha... more The in-field critical current of commercial YBa2Cu3O7 coated conductors can be substantially enhanced by post-fabrication irradiation with 4 MeV protons. Irradiation to a fluence of 8 × 1016 p/cm2 induces a near doubling of the critical current in fields of 6 T || c at a temperature of 27 K, a field and temperature range of interest for applications, such as rotating machinery. A mixed pinning landscape of preexisting precipitates and twin boundaries and small, finely dispersed irradiation induced defects may account for the improved vortex pinning in high magnetic fields. Our data indicate that there is significant head-room for further enhancements.
IEEE Transactions on Applied Superconductivity, 2007
Second Generation (2G) YBCO High Temperature Superconductor wire, based on the RABiTS/MOD process... more Second Generation (2G) YBCO High Temperature Superconductor wire, based on the RABiTS/MOD process, is now being produced in continuous lengths at American Superconductor (AMSC) using a full-scale, reel-to-reel manufacturing line. AMSC's approach for manufacturing 2G wire is designed around a low-cost, wide-strip technology, in which a 4-cm wide strip is slit into multiple narrower wires, then laminated to metallic stabilizers producing a 3-ply wire called 344 superconductors. A major advantage of this approach is the ability to tailor the electrical, mechanical and thermal properties and dimensions of the final wire for specific applications and operating conditions. This allows the final wire properties to be tuned for targeted applications, including cables and fault current limiters, by tailoring the resistivity and thickness of the stabilizer layers. The superconducting properties of the MOD-based YBCO are also being improved by the introduction of thicker YBCO layers and improved flux pinning centers. This paper describes the present status of 2G wire manufacturing at AMSC, reviews present and projected performance of the 344 superconductors, and summarizes initial application demonstrations utilizing 344 superconductors.
Applied Physics Letters, 2006
The density n of stacking faults (SFs) in epitaxial YBa2Cu3O7−x (Y123) films, consisting of extra... more The density n of stacking faults (SFs) in epitaxial YBa2Cu3O7−x (Y123) films, consisting of extra CuO planes, is measured by fitting x-ray diffraction patterns using a random stacking model. The SF density is n=0.068nm−1 in films grown by metal-organic deposition on textured templates and optimized for high Ic. The presence of SF is correlated with pinning of magnetic field (H) applied in the Y123 ab plane. SF can be nearly eliminated by a high temperature anneal, or by adding excess Dy, resulting in Ic which is nearly independent of the orientation of H.
Journal of the American Ceramic Society, 2001
We examined the static axial displacement of a ceramic d 31-gradient flextensional transducer bot... more We examined the static axial displacement of a ceramic d 31-gradient flextensional transducer both experimentally and theoretically. Two lead zirconate titanate systems, (PZT)/PZT and PZT/ZnO, were studied. The PZT/PZT transducers consisted of two PZT layers of different d 31 coefficients. The PZT/ZnO transducers consisted of a PZT and a ZnO layer. The PZT/PZT transducers were of an inner-type dome structure. The PZT/ZnO transducers were either flat, or had an inner-or outer-type dome structure by varying the thickness ratio between the two layers or the Sb 2 O 3 content in the ZnO layer. An inner (outer)-type transducer has the large-d 31 layer on the inside (outside) of the dome structure. For the PZT/PZT transducers, the axial displacement varied with the thickness ratio and reached a maximum when the two layers had similar thickness, in agreement with the calculations. With a conductive nonpiezoelectric layer, the PZT/ZnO transducers had higher axial displacements, which varied with the thickness ratio and the Sb 2 O 3 content, than the PZT/PZT transducers. With 6 wt% Sb 2 O 3 , the transducers were flat and the measured displacements at various thickness ratios were similar to the calculated values. With 4 wt% Sb 2 O 3 , the transducers were of an outer type. The measured axial displacements were about twice the calculated values, suggesting an enhanced d 31 value because of the tensile bending stress in the PZT layer. The scaled axial displacements of the PZT/ZnO transducers with 4 wt% Sb 2 O 3 were comparable to that of the Rainbow transducers. With 8 wt% Sb 2 O 3 , the displacements of transducers with thin PZT layers (<0.3 mm) were lower than the calculated values because of increased conductivity in the PZT layer.
Superconductor Science and Technology, 2007
ABSTRACT The microstructure of metal-organic deposited YBa2Cu3O7−δ with dysprosium (Dy) additions... more ABSTRACT The microstructure of metal-organic deposited YBa2Cu3O7−δ with dysprosium (Dy) additions has been investigated by transmission electron microscopy (TEM). Dy additions which increase the density of normal-state nanoparticles in the YBCO have been demonstrated to enhance the critical current densities in moderate magnetic fields. The influence of nanoparticles, stacking faults and other planar defects on flux pinning is discussed. We observed a high density of nanoparticles in the size range of 10–50 nm, which may act as flux pinning centres to enhance the critical current density of the material. Stacking faults and planar defects are observed which may also be effective flux pinning centres in YBCO samples with and without Dy addition.
Physica C: Superconductivity and its Applications, 2006
RABiTS based metal-organic deposition (MOD) buffer/YBa2Cu3O7−δ (YBCO) approach has been considere... more RABiTS based metal-organic deposition (MOD) buffer/YBa2Cu3O7−δ (YBCO) approach has been considered as one of the potential, low-cost approaches to fabricate high performance second generation coated conductors. The most commonly used RABiTS architectures consisting of a starting template of biaxially textured Ni–W (5 at.%) substrate with a seed layer of Y2O3, a barrier layer of YSZ, and a CeO2 cap. In
Physica C: Superconductivity, 2009
American Superconductor Corporation (AMSC) has developed the base technology and a manufacturing ... more American Superconductor Corporation (AMSC) has developed the base technology and a manufacturing line for initial volume production of low-cost second generation high temperature superconductor (2G HTS) wire for commercial and military applications. The manufacturing line is based on reel-to-reel processing of wide HTS strips using rolling assisted bi-axially textured substrate (RABiTS TM) for the template and Metal Organic Deposition (MOD) for the HTS layer. AMSC's wide strip process is a low cost manufacturing technology since multiple wires are produced in a single manufacturing pass by slitting the wide strip to narrower width in the last stage of the manufacturing process. Industry standard 4.4 mm wide wires are produced by laminating metallic foils, such as copper, stainless steel or any other material, to the HTS insert wire, and are chosen to tailor the electrical, thermal and mechanical properties of the wire for specific applications. The laminated, 4.4 mm wide wires are known as ''344 superconductors." In this paper, we summarize the status of AMSC's manufacturing capability, the performance of the wire presently being produced, as well as the cost and technical advantages of AMSC's manufacturing approach. In addition, future direction for research and development to improve electrical performance is presented.
Journal of the American Ceramic Society, 1999
We have examined the static and dynamic electromechanical responses of PZT-brass (piezoelectric-n... more We have examined the static and dynamic electromechanical responses of PZT-brass (piezoelectric-nonpiezoelectric) plate unimorphs of various brass/PZT thickness ratios. The study was performed both experimentally and theoretically. The static measurements showed that, given a PZT layer thickness, there exists a brass/PZT thickness ratio that gives the unimorph the highest static displacement under an applied field. The effects of geometric shape and external loading on the displacement of the unimorphs were also examined. The dynamic measurements showed that, given a PZT layer thickness, the bending-mode resonance frequencies increase with an increasing brass/PZT thickness ratio. These results were in good agreement with the theoretical predictions that were obtained with the plate geometry.
Journal of Materials Research, 2009
We analyzed the crystallographic c-axis tilt of (001) Y2O3 films grown on biaxially textured Ni–5... more We analyzed the crystallographic c-axis tilt of (001) Y2O3 films grown on biaxially textured Ni–5%W tapes under different oxygen flux conditions. Results show that different tilting mechanisms were effective in films with different oxygen stoichiometry. Moreover, the structure of the film/substrate interface investigated by transmission electron microscopy, and the residual strain of the film investigated by x-ray diffraction were also dependent on the film oxygen content. Although the oxygen stoichiometric Y2O3 sample exhibited a coherent film/substrate interface and the sharpest out-of-plane texture, the films grown under reduced oxygen pressure exhibited a smaller overall c-axis tilt due to formation of interface dislocations and regions in which the film oxygen vacancies ordered to form a lattice superstructure.
Journal of Applied Physics, 2007
It has been well established that the critical current density J c across grain boundaries ͑GBs͒ ... more It has been well established that the critical current density J c across grain boundaries ͑GBs͒ in high-temperature superconductors decreases exponentially with misorientation angle beyond ϳ2°-3°. This rapid decrease is due to a suppression of the superconducting order parameter at the grain boundary, giving rise to weakly pinned Abrikosov-Josephson ͑AJ͒ vortices. Here we show that if the GB plane meanders, this exponential dependence no longer holds, permitting greatly enhanced J c values: up to six times at 0 T and four times at 1 T at ϳ 4°-6°. This enhancement is due to an increase in the current-carrying cross section of the GBs and the appearance of short AJ vortex segments in the GB plane, confined by the interaction with strongly pinned Abrikosov ͑A͒ vortices in the grains.
IEEE Transactions on Applied Superconductivity, 2007
Two different types of defect structures have been identified to be responsible for the enhanced ... more Two different types of defect structures have been identified to be responsible for the enhanced pinning in metal organic deposited YBCO films. Rare earth additions result in the formation of nanodots in the YBCO matrix, which form uncorrelated pinning centers, increasing pinning in all magnetic field orientations. 124-type intergrowths, which form as laminar structures parallel to the ab-plane, are responsible
IEEE Transactions on Appiled Superconductivity, 2005
Sharpening of the substrate texture is key to obtain critical current densities approaching singl... more Sharpening of the substrate texture is key to obtain critical current densities approaching single crystal values in coated conductors. In particular, great improvements in c are obtained by narrowing the substrate texture down to values of 3-4 for both phi-scan and omega-scan FWHM. The best Ni-alloy substrates used today for RABiTS show FWHM's of 6-5. Although the majority of buffer layers deposited on these tapes by various techniques approximately duplicate the substrate's grain alignment, some materials have been found to develop much sharper out-of-plane texture. Here we report on growth and structural characterization of TiN seed layers on various textured metal tapes. TiN seed layers deposited by PLD have consistently shown tilting of the-axis toward the direction of the sample's surface normal. We address the extent of such tilt and discuss feasibility of alternative RABiTS architectures that use a TiN seed layer to provide very sharp out-of-plane texture and serve as an effective metal-ion diffusion barrier.
IEEE Journal of Photovoltaics
In-situ Cd-saturated growth of polycrystalline CdTe:As thin film was performed by metal organic c... more In-situ Cd-saturated growth of polycrystalline CdTe:As thin film was performed by metal organic chemical vapour deposition at a low temperature of 350°C, to investigate the impact on As doping and device V OC. Device characterization showed conversion efficiency of ∼14%, and V OC of 772 mV, which is an improvement to the baseline device with CdTe:As absorber layer grown at 390°C under non-saturated conditions. When the low temperature Cd-saturated growth was combined with chlorine heat treatment at a higher temperature of 440°C (in contrast with the standard 420°C) for 10 min, device efficiency improved to ∼17% with a high V OC of 877 mV. As a result, ∼100 mV boost in V OC from baseline is demonstrated with Cd-saturated CdTe:As device. Micro-photoluminescence and time-resolved photoluminescence measurements performed on these Cd-saturated CdTe:As devices confirmed that minority carrier lifetime significantly improved.
2022 IEEE 49th Photovoltaics Specialists Conference (PVSC)
In-situ Cd-saturated growth of polycrystalline CdTe:As thin film was performed by metal organic c... more In-situ Cd-saturated growth of polycrystalline CdTe:As thin film was performed by metal organic chemical vapour deposition at a low temperature of 350°C, to investigate the impact on As doping and device V OC. Device characterization showed conversion efficiency of ∼14%, and V OC of 772 mV, which is an improvement to the baseline device with CdTe:As absorber layer grown at 390°C under non-saturated conditions. When the low temperature Cd-saturated growth was combined with chlorine heat treatment at a higher temperature of 440°C (in contrast with the standard 420°C) for 10 min, device efficiency improved to ∼17% with a high V OC of 877 mV. As a result, ∼100 mV boost in V OC from baseline is demonstrated with Cd-saturated CdTe:As device. Micro-photoluminescence and time-resolved photoluminescence measurements performed on these Cd-saturated CdTe:As devices confirmed that minority carrier lifetime significantly improved.
Superconductor Science and Technology, 2006
We report on the thickness dependence of the superconducting characteristics including critical c... more We report on the thickness dependence of the superconducting characteristics including critical current I c , critical current density J c , transition temperature T c , irreversibility field H irr , bulk pinning force plot F p (H), and the normal state resistivity curve ρ(T) measured after successive ion milling of ~ 1 µm thick high I c YBa 2 Cu 3 O 7-x films made by an ex situ metal-organic deposition process on Ni-W rolling-assisted biaxially textured substrates (RABiTS TM). Contrary to many recent data, mostly on in situ pulsed laser deposition (PLD) films, which show strong depression of J c with increasing film thickness t, our films exhibit only a weak dependence of J c on t. The two better textured samples had full cross-section average J c,avg (77K,0T) ~ 4 MA/cm 2 near the buffer layer interface and ~3 MA/cm 2 at full thickness, despite significant current blocking due to ~30% porosity in the film. Taking account of the thickness dependence of the porosity, we estimate that the local, vortex-pinning current density is essentially independent of thickness, while accounting for the additional current-blocking effects of grain boundaries leads to local, vortex-pinning J c values well above 5 MA/cm 2. Such high local J c values are produced by strong three-dimensional vortex pinning which subdivides vortex lines into weakly coupled segments much shorter than the film thickness.
Microscopy and Microanalysis, 2010
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, ... more Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.
Journal of Physics: Conference Series, 2014
AMSC produces Second Generation (2G) HTS wire for utility power applications as well as coil, mot... more AMSC produces Second Generation (2G) HTS wire for utility power applications as well as coil, motor and generator solutions. In this paper, various types of AMSC's Amperium ® wire suitable to power cables, fault current limiters and coils are reviewed. In addition, recently developed performance-improvements in amperage, reduced ac power loss and mechanical properties are summarized. The introduction of thicker HTS layers coupled with optimized heat treatments to enhance critical current density dramatically improve both cable and coil wire current-carrying capability. A non-magnetic RABiTS TM substrate has now been developed to the point where it is compatible with the manufacturing process and capable of sustaining large critical currents. Finally, the ability of Amperium ® wires to withstand cable-winding stresses, and to exhibit the high transverse c-axis strength critical to the reliability of the wire in coils, are discussed.
Journal of Materials Research, 2005
Chemical solution processing of Gd2Zr2O7 (GZO) thin films via sol-gel and metalorganic decomposit... more Chemical solution processing of Gd2Zr2O7 (GZO) thin films via sol-gel and metalorganic decomposition (MOD) precursor routes have been studied on textured Ni-based tape substrates. Even though films processed by both techniques showed similar property characteristics, the MOD-derived samples developed a high degree of texture alignment at significantly lower temperatures. Both precursor chemistries resulted in exceptionally dense, pore-free, and smooth microstructures, reflected in the cross-sectional and plan-view high-resolution scanning and transmission electron microscopy studies. On the MOD GZO buffered Ni–3at.% W (Ni–W) substrates with additional CeO2/YSZ sputtered over layers, a 0.8-μm-thick YBa2Cu3O7−δ (YBCO) film, grown by an ex situ metalorganic trifluoroacetate precursor method, yielded critical current, Ic (77 K, self-field), of 100 A/cm width. Furthermore, using pulsed-laser deposited YBCO films, a zero-field superconducting critical current density, Jc (77 K), of 1 × 10...
Applied Physics Letters, 2007
The authors find the critical current anisotropy of a bilayer YBa2Cu3O7−δ film with different pin... more The authors find the critical current anisotropy of a bilayer YBa2Cu3O7−δ film with different pinning structures in each layer is the sum of the anisotropy of the two individual layers, revealing that it is possible to tune the anisotropy of the composite through variation of an individual layer’s thickness and pinning structure. YBa2Cu4Ox intergrowths and Dy2O3 nanodots were the dominant pinning structures in the top and bottom layers, respectively. The bottom layer of the composite was isolated using traditional Ar+ ion milling and the top layer was isolated using a focused ion beam, allowing each layer to be studied independently.
Applied Physics Letters, 2013
The in-field critical current of commercial YBa2Cu3O7 coated conductors can be substantially enha... more The in-field critical current of commercial YBa2Cu3O7 coated conductors can be substantially enhanced by post-fabrication irradiation with 4 MeV protons. Irradiation to a fluence of 8 × 1016 p/cm2 induces a near doubling of the critical current in fields of 6 T || c at a temperature of 27 K, a field and temperature range of interest for applications, such as rotating machinery. A mixed pinning landscape of preexisting precipitates and twin boundaries and small, finely dispersed irradiation induced defects may account for the improved vortex pinning in high magnetic fields. Our data indicate that there is significant head-room for further enhancements.
IEEE Transactions on Applied Superconductivity, 2007
Second Generation (2G) YBCO High Temperature Superconductor wire, based on the RABiTS/MOD process... more Second Generation (2G) YBCO High Temperature Superconductor wire, based on the RABiTS/MOD process, is now being produced in continuous lengths at American Superconductor (AMSC) using a full-scale, reel-to-reel manufacturing line. AMSC's approach for manufacturing 2G wire is designed around a low-cost, wide-strip technology, in which a 4-cm wide strip is slit into multiple narrower wires, then laminated to metallic stabilizers producing a 3-ply wire called 344 superconductors. A major advantage of this approach is the ability to tailor the electrical, mechanical and thermal properties and dimensions of the final wire for specific applications and operating conditions. This allows the final wire properties to be tuned for targeted applications, including cables and fault current limiters, by tailoring the resistivity and thickness of the stabilizer layers. The superconducting properties of the MOD-based YBCO are also being improved by the introduction of thicker YBCO layers and improved flux pinning centers. This paper describes the present status of 2G wire manufacturing at AMSC, reviews present and projected performance of the 344 superconductors, and summarizes initial application demonstrations utilizing 344 superconductors.
Applied Physics Letters, 2006
The density n of stacking faults (SFs) in epitaxial YBa2Cu3O7−x (Y123) films, consisting of extra... more The density n of stacking faults (SFs) in epitaxial YBa2Cu3O7−x (Y123) films, consisting of extra CuO planes, is measured by fitting x-ray diffraction patterns using a random stacking model. The SF density is n=0.068nm−1 in films grown by metal-organic deposition on textured templates and optimized for high Ic. The presence of SF is correlated with pinning of magnetic field (H) applied in the Y123 ab plane. SF can be nearly eliminated by a high temperature anneal, or by adding excess Dy, resulting in Ic which is nearly independent of the orientation of H.
Journal of the American Ceramic Society, 2001
We examined the static axial displacement of a ceramic d 31-gradient flextensional transducer bot... more We examined the static axial displacement of a ceramic d 31-gradient flextensional transducer both experimentally and theoretically. Two lead zirconate titanate systems, (PZT)/PZT and PZT/ZnO, were studied. The PZT/PZT transducers consisted of two PZT layers of different d 31 coefficients. The PZT/ZnO transducers consisted of a PZT and a ZnO layer. The PZT/PZT transducers were of an inner-type dome structure. The PZT/ZnO transducers were either flat, or had an inner-or outer-type dome structure by varying the thickness ratio between the two layers or the Sb 2 O 3 content in the ZnO layer. An inner (outer)-type transducer has the large-d 31 layer on the inside (outside) of the dome structure. For the PZT/PZT transducers, the axial displacement varied with the thickness ratio and reached a maximum when the two layers had similar thickness, in agreement with the calculations. With a conductive nonpiezoelectric layer, the PZT/ZnO transducers had higher axial displacements, which varied with the thickness ratio and the Sb 2 O 3 content, than the PZT/PZT transducers. With 6 wt% Sb 2 O 3 , the transducers were flat and the measured displacements at various thickness ratios were similar to the calculated values. With 4 wt% Sb 2 O 3 , the transducers were of an outer type. The measured axial displacements were about twice the calculated values, suggesting an enhanced d 31 value because of the tensile bending stress in the PZT layer. The scaled axial displacements of the PZT/ZnO transducers with 4 wt% Sb 2 O 3 were comparable to that of the Rainbow transducers. With 8 wt% Sb 2 O 3 , the displacements of transducers with thin PZT layers (<0.3 mm) were lower than the calculated values because of increased conductivity in the PZT layer.
Superconductor Science and Technology, 2007
ABSTRACT The microstructure of metal-organic deposited YBa2Cu3O7−δ with dysprosium (Dy) additions... more ABSTRACT The microstructure of metal-organic deposited YBa2Cu3O7−δ with dysprosium (Dy) additions has been investigated by transmission electron microscopy (TEM). Dy additions which increase the density of normal-state nanoparticles in the YBCO have been demonstrated to enhance the critical current densities in moderate magnetic fields. The influence of nanoparticles, stacking faults and other planar defects on flux pinning is discussed. We observed a high density of nanoparticles in the size range of 10–50 nm, which may act as flux pinning centres to enhance the critical current density of the material. Stacking faults and planar defects are observed which may also be effective flux pinning centres in YBCO samples with and without Dy addition.
Physica C: Superconductivity and its Applications, 2006
RABiTS based metal-organic deposition (MOD) buffer/YBa2Cu3O7−δ (YBCO) approach has been considere... more RABiTS based metal-organic deposition (MOD) buffer/YBa2Cu3O7−δ (YBCO) approach has been considered as one of the potential, low-cost approaches to fabricate high performance second generation coated conductors. The most commonly used RABiTS architectures consisting of a starting template of biaxially textured Ni–W (5 at.%) substrate with a seed layer of Y2O3, a barrier layer of YSZ, and a CeO2 cap. In
Physica C: Superconductivity, 2009
American Superconductor Corporation (AMSC) has developed the base technology and a manufacturing ... more American Superconductor Corporation (AMSC) has developed the base technology and a manufacturing line for initial volume production of low-cost second generation high temperature superconductor (2G HTS) wire for commercial and military applications. The manufacturing line is based on reel-to-reel processing of wide HTS strips using rolling assisted bi-axially textured substrate (RABiTS TM) for the template and Metal Organic Deposition (MOD) for the HTS layer. AMSC's wide strip process is a low cost manufacturing technology since multiple wires are produced in a single manufacturing pass by slitting the wide strip to narrower width in the last stage of the manufacturing process. Industry standard 4.4 mm wide wires are produced by laminating metallic foils, such as copper, stainless steel or any other material, to the HTS insert wire, and are chosen to tailor the electrical, thermal and mechanical properties of the wire for specific applications. The laminated, 4.4 mm wide wires are known as ''344 superconductors." In this paper, we summarize the status of AMSC's manufacturing capability, the performance of the wire presently being produced, as well as the cost and technical advantages of AMSC's manufacturing approach. In addition, future direction for research and development to improve electrical performance is presented.
Journal of the American Ceramic Society, 1999
We have examined the static and dynamic electromechanical responses of PZT-brass (piezoelectric-n... more We have examined the static and dynamic electromechanical responses of PZT-brass (piezoelectric-nonpiezoelectric) plate unimorphs of various brass/PZT thickness ratios. The study was performed both experimentally and theoretically. The static measurements showed that, given a PZT layer thickness, there exists a brass/PZT thickness ratio that gives the unimorph the highest static displacement under an applied field. The effects of geometric shape and external loading on the displacement of the unimorphs were also examined. The dynamic measurements showed that, given a PZT layer thickness, the bending-mode resonance frequencies increase with an increasing brass/PZT thickness ratio. These results were in good agreement with the theoretical predictions that were obtained with the plate geometry.
Journal of Materials Research, 2009
We analyzed the crystallographic c-axis tilt of (001) Y2O3 films grown on biaxially textured Ni–5... more We analyzed the crystallographic c-axis tilt of (001) Y2O3 films grown on biaxially textured Ni–5%W tapes under different oxygen flux conditions. Results show that different tilting mechanisms were effective in films with different oxygen stoichiometry. Moreover, the structure of the film/substrate interface investigated by transmission electron microscopy, and the residual strain of the film investigated by x-ray diffraction were also dependent on the film oxygen content. Although the oxygen stoichiometric Y2O3 sample exhibited a coherent film/substrate interface and the sharpest out-of-plane texture, the films grown under reduced oxygen pressure exhibited a smaller overall c-axis tilt due to formation of interface dislocations and regions in which the film oxygen vacancies ordered to form a lattice superstructure.
Journal of Applied Physics, 2007
It has been well established that the critical current density J c across grain boundaries ͑GBs͒ ... more It has been well established that the critical current density J c across grain boundaries ͑GBs͒ in high-temperature superconductors decreases exponentially with misorientation angle beyond ϳ2°-3°. This rapid decrease is due to a suppression of the superconducting order parameter at the grain boundary, giving rise to weakly pinned Abrikosov-Josephson ͑AJ͒ vortices. Here we show that if the GB plane meanders, this exponential dependence no longer holds, permitting greatly enhanced J c values: up to six times at 0 T and four times at 1 T at ϳ 4°-6°. This enhancement is due to an increase in the current-carrying cross section of the GBs and the appearance of short AJ vortex segments in the GB plane, confined by the interaction with strongly pinned Abrikosov ͑A͒ vortices in the grains.
IEEE Transactions on Applied Superconductivity, 2007
Two different types of defect structures have been identified to be responsible for the enhanced ... more Two different types of defect structures have been identified to be responsible for the enhanced pinning in metal organic deposited YBCO films. Rare earth additions result in the formation of nanodots in the YBCO matrix, which form uncorrelated pinning centers, increasing pinning in all magnetic field orientations. 124-type intergrowths, which form as laminar structures parallel to the ab-plane, are responsible
IEEE Transactions on Appiled Superconductivity, 2005
Sharpening of the substrate texture is key to obtain critical current densities approaching singl... more Sharpening of the substrate texture is key to obtain critical current densities approaching single crystal values in coated conductors. In particular, great improvements in c are obtained by narrowing the substrate texture down to values of 3-4 for both phi-scan and omega-scan FWHM. The best Ni-alloy substrates used today for RABiTS show FWHM's of 6-5. Although the majority of buffer layers deposited on these tapes by various techniques approximately duplicate the substrate's grain alignment, some materials have been found to develop much sharper out-of-plane texture. Here we report on growth and structural characterization of TiN seed layers on various textured metal tapes. TiN seed layers deposited by PLD have consistently shown tilting of the-axis toward the direction of the sample's surface normal. We address the extent of such tilt and discuss feasibility of alternative RABiTS architectures that use a TiN seed layer to provide very sharp out-of-plane texture and serve as an effective metal-ion diffusion barrier.