Top-seeded Melt Growth Research Articles

Improving Mechanical Strength of YBCO Bulk Superconductors by Addition of Ag

The widespread use of ceramic (RE)Ba 2 Cu 3 O 7 bulk superconductors (RE-123), where RE = Y, Gd, or Sm, is generally hindered by their poor mechanical properties. While a large number of techniques can be used to improve the mechanical properties of conventional ceramic materials, many of these are incompatible with the growth of single grain, bulk RE-123 superconductors using the top seeded melt growth (TSMG) process. Complications arise due to the need to minimize the degradation of the superconducting properties and produce a single-grained sample. Nonetheless, the addition of Ag to RE-Ba-Cu-O [(RE)BCO] precursor powder has been demonstrated to be effective in improving the mechanical properties of single grain bulk superconductors fabricated by TSMG without deleterious effects on performance. Although large single grains of GdBa 2 Cu 3 O 7 -Ag and SmBa 2 Cu 3 O 7 -Ag have been successfully and reliably grown, it has proven more difficult to grow large single grains of YBa 2 Cu 3 O 7 -Ag. We recently demonstrated the growth of single grain YBa 2 Cu 3 O 7 -Ag bulk superconductors that exhibit relatively good superconducting properties. In this work, we report the flexural stress at a number of locations within YBa 2 Cu 3 O 7 single grains grown by TSMG with and without additional liquid phase and with silver addition. In addition, we have compared the distribution of the failure stress with the pore and silver distribution.

Enhanced Mechanical Properties of Single-Domain YBCO Bulk Superconductors Processed With Artificial Holes

Single domain YBCO bulk superconductors were prepared using a conventional top-seeded melt growth technique. Artificial holes were introduced to the green sample prior to thermal processing using a bespoke “spiked” mould. Mechanical properties such as elastic modulus, Vickers hardness, compressive strength, and tensile strength were measured and compared to the properties of a standard bulk. The presence of the holes the bulk microstructure was observed to limit porosity and lower the concentration of macro-cracks in the bulk microstructure, resulting in significantly enhanced mechanical properties of the bulk single grains. The elastic modulus of the perforated bulks was observed to exhibit an increase of more than 45% compared to the standard samples. Compressive and tensile strengths were also improved significantly in the samples containing artificial holes. Observed differences in Vickers hardness, on the other hand, were negligible. This could be because of the fact that the hardness is measured on a small surface area of the single grain sample, where the effect of lower porosity and lower concentration of macro-cracks is less relevant. The introduction of artificial holes to the bulk, single grain microstructure appears to be a very promising technology for the production of melt-textured bulk superconductors with enhanced mechanical properties.

An analysis on the relation between the seed distance and vertical levitation force for the multi−seeded YBCO using the modified advanced frozen image (MAFI) and experimental methods

The higher magnetic levitation force and related stiffness values are very important for Maglev and magnetic bearing applications. Also, larger superconducting surface area is needed for continuous and larger magnetic mediums with different geometries and dimensions in real scale industrial applications of superconducting systems. In this study, the cylindrical YBCO superconductors were fabricated by top−seeded melt growth (TSMG) method in single and two−seeded forms with different seed distances and then the magnetic force and stiffness measurements were carried out by three axes magnetic force measurement system in different cooling heights (CH) of 20 mm and 75 mm. Additionally, a new analytical method, based on the magnetic dipole approximation, is proposed to calculate the levitation force in this study, named as Modified Advanced Frozen Image Method (MAFI), since although the Advanced Frozen Image Method in literature can calculate the levitation force with hysteresis, this method does not include the size effect of the superconductor. In the experimental studies, it is seen that the maximum levitation force values obtained by PMG with three PMs (named PMG−1) are more than two times higher than that of obtained with single PM for all samples with different distance of seeds, because of the higher magnetic flux distribution of related PMG arrangement than the single PM. In addition, the maximum magnetic levitation force value firstly increased and then decreased due to current coupling effect weakness by increasing distance of seeds. The calculated analytical levitation force results are not compatible with the experimental results without current coupling effect, but a well agreement is observed when the current coupling effect is taken into account in calculations. Also the MAFI method was tested with different dimensions of superconductors and the obtained results indicated the success of the proposed method. The maximum levitation force values obtained with MAFI method increased with increasing dimensions of HTS and PMs. Thus, one can say that the MAFI method is useful for the levitation force calculations between multi−seeded superconductors and PMGs with different dimensions and for different CHs. As a result, the analytical levitation force values obtained with the MAFI method are agree with the experimental levitation force sufficiently and this method can give fast calculation results without any divergence problem. This method can be thought as an alternative to the numerical calculation methods, having serious divergence problems for much amount and bigger size superconducting samples, therefore it will be useful to clarify bulk superconducting properties as supporter to the experimental studies.

Comparison of the superconducting properties of Y-Ba-Cu-O and Y-Ba-Cu-O-Ag bulk superconductors

The widespread use of RE-Ba-Cu-O [(RE)BCO] bulk superconductors, where RE=Y, Gd or Sm, in practical applications requires large single grains that exhibit uniform superconducting properties. Until recently, however, it was difficult to grow successfully YBCO-Ag bulk materials in the required single grain form, due primarily to the relative complexity of the top seeded melt growth process (TSMG) and the introduction of an alloying element (Ag) to the precursor composition. In most cases, alloying elements are used to improve the mechanical properties of the bulk superconductor whilst, at the same time, aim to cause minimal detrimental effect on the superconducting properties of the fully processed sample. In this work we investigate the effect of the addition of silver to YBCO on the superconducting properties of the bulk single grain, including trapped field, Tc and Jc, and on the sample microstructure.

Magnetic Shielding of Open and Semi-closed Bulk Superconductor Tubes: The Role of a Cap

In this paper we investigate the magnetic shielding of hollow and semi-closed bulk superconducting tubes at 77 K. We first consider the properties of a commercial Bi-2223 tube closed by a disk-shaped cap placed against its extremity. The results are compared with those obtained on a bulk large grain Y-Ba-Cu-O (YBCO) tube produced by buffer-aided top seeded melt growth. In this process, the disk-shaped pellet and the tubular sample are grown together, resulting in a tube naturally closed at one extremity. The field to be shielded is either parallel or perpendicular to the main axis of the tube. The experimental results are compared with the results of finite element numerical modeling carried out either in two dimensions (for the axial configuration) or three dimensions (for the transverse configuration). In the axial configuration, the results show that the shielded volume can be enhanced easily by increasing the thickness of the cap. In the transverse configuration, the results show the critical role played by the superconducting current loops flowing between the tube and the cap for magnetic shielding. If the tube and the cap are separated by a non-superconducting joint or air gap, the presence of a cap leads only to a small improvement of the transverse shielding factor, even for a configuration where the gap between the cap and the tube contains a 90° bend. The cap leads to a significant increase in the transverse shielding when the cap and the tube are naturally grown in the same process, i.e., made of a continuous superconducting material. The experimental results can be reproduced qualitatively by 3-D numerical modeling.

Growth, Microstructure, and Properties of GdBCO–Ag Superconductor

We prepared GdBa2Cu3O7−δ (Gd123, GdBCO) single-grain bulk with Ag addition via the top-seeded melt growth method. Peritectic temperatures of precursor powder mixture and pure Gd123 powder were tested by differential thermal analysis (DTA). The dependence of the volume fraction and the size of Gd2BaCuO5 (Gd211) particles on the distance from the seed was determined with the help of image processing of the micrographs taken by a scanning electron microscope (SEM) from the polished a/c-section of the sample. The morphology of Ag particles was evaluated by the SEM image analysis. The substitution of Ag in Gd123 was characterized by the wavelength-dispersive spectrometry. The magnetic measurements of superconducting properties (critical current density Jc at 77 K and critical temperature Tc ) were carried out using a vibrating sample magnetometer. Magnetization measurements were performed on the specimens taken from several different locations of the same crystal plane and the value of the maximum middle critical temperature ( Tc,m ) was determined as 92.6 K.

Cost-effective isothermal top-seeded melt-growth of single-domain YBCO superconducting ceramics

In this work, a series of melt processed YBaCuO (YBCO) single-grains have been fabricated by the top-seeded melt growth (TSMG) technique. The melt processing is accepted widely as an effective way to grow bulk, single grain YBCO superconductors; however, this process is extremely complex and every step can affect the final properties of prepared bulk. Therefore, the impact of precursor powder preparation and growth conditions was studied for the first time. Cost-effective in-house made powder and commercially available precursor powders were employed and samples were grown employing top seeded melt growth, following the isothermal and the under-cooling growth techniques. The bulk microstructure including Y2BaCuO5 (Y-211) particle size and distribution, superconducting properties (Tc, Jc) and field trapping potential were investigated. The cost-effective high performance batch processing methodology was optimized. The fabricated YBCO bulks (diameter of 28 mm) exhibited average trapped field of 0.85 T at 77 K. Furthermore, other possibilities to achieve advancement in processing (RE)BCO bulks, are proposed.

Magnetic properties of the welded joined TSMG Y123 + x wt% Y211 (x = 20 and 30) bulk superconductors

Although the welding techniques have been used to join for bulk YBCO superconductors with a sintered superconductor, similar technique as a Ag2O added bulk YBCO superconductor fabricated by melt-powder-melt-growth process (MPMG) for using as a solder material has not been used, until now. Also, physical and the bulk superconducting properties of the welded samples have not been investigated. In this study, two 20 wt% Y211 and two 30 wt% Y211 added YBCO main samples were fabricated by cold top seeding-melt-growth (TSMG) method by using an Nd123 seed. Two main samples having the same Y211 addition and welding sample positioned between the main samples stacked and welded thermally with a pressure source simultaneously. It can be seen from the levitation force measurement, making before the welding process, that the 30 wt% Y211 added samples have the larger the maximum repulsive forces values than the 20 wt% Y211 added and Ag2O added welding samples but at the same order. After the welding process the welded samples cut into the specimens, to investigate micro structure and electromagnetic properties, positioned above, on and below of the welding region of the each welded Y123 samples. From the SEM analysis a continuous structural phase was obtained between the solder material and the main samples with a good integration without any boundary gap or defects. The welding process had no negative noticeable effect on Tc of the samples under zero magnetic field, while superconducting transition width (∆Tc) of the specimen cutting from the 30 wt% Y211 added sample (Y30-ab) is smaller the specimen cutting from the 20 wt% Y211 added sample (Y20-ab) under applied magnetic field points out that Y30-ab is more resistant to the applied field than the Y20-ab because of the 211 addition. In addition, 30 wt% 211 addition ratio is more efficient for welding region and whole welded sample in terms of the supplying uniform superconducting properties as Jc. The obtained results on welded joined bulk superconductor can be beneficial to increase application potential of these superconducting materials in real scale magnetic systems.

Synthesis of Y2BaCuO5 nano-whiskers by a solution blow spinning technique and their successful introduction into single-grain, YBCO bulk superconductors

The ability of single grain Y-Ba-Cu-O (YBCO) bulk superconductors to trap large magnetic fields is due generally to the presence of embedded, non-superconducting Y2BaCuO5 (Y-211) phase particles, in optimum amount, in the superconducting YBa2Cu3O7-δ (Y-123) phase matrix, which increases flux pinning and, hence, critical current density of the bulk material. The presence of smaller particles of Y-211 could be expected to improve further the superconducting properties of single grain, bulk YBCO samples, although the smallest Y-211 particles that have been engineered to date within the bulk microstructure are around 800 nm in size. It is extremely challenging to reduce the Y-211 particle size any further due to problems of particle agglomeration that originate, inevitably, from the effects of surface energy and reactivity at relatively high processing temperatures. In this work, we report a novel approach to the fabrication of Y-211 pinning centres in bulk YBCO superconductors in the form of nano-whiskers manufactured by a solution blow spinning technique. The Y-211 nano-whiskers, of which 62% were smaller than 500 nm, were added to the YBCO precursor powders to produce a single grain bulk sample by the buffer-aided top-seeded melt growth (BA-TSMG) processing technique. The resulting YBCO single grain, of diameter 20 mm, was able to trap a magnetic field of 0.63 T at 77 K with an associated critical current density of 3.9 × 104 A/cm2 in self-field. The results of this study demonstrate clearly that the use of Y-211 nano-whiskers is a promising route for enhancing flux pinning in bulk YBCO single-grains, which is potentially significant for the development of high field engineering applications.

Influence of Sm Doping on YBCO Bulks in YBa2Cu3O7-δ/Y2 BaCuO5 System

Sm-doped single-grain YBCO bulk superconductors were fabricated by the Top Seeded Melt Growth process in the system YBa 2 Cu 3 O 7-δ /Y 2 BaCuO 5 with CeO 2 addition and with added liquid-rich powder at the bottom pellet. According to microstructure analyses, Sm 2 O 3 addition led to the refinement of Y-211 particles, which was reflected in higher critical current density, J c , at 77 K and zero field measured for doped sample. Missing of expected secondary peak in J c field dependence for doped sample was related to lowering of Sm concentration in the sample by its diffusion into additional liquid-rich phase pellet. Sm-doped pellet exhibited higher maximum trapped field, B c , measured at 77 K.

A Low-Cost Fabrication Technique for the Growth of Single-Domain GdBCO Bulk Superconductor from Raw Metal Oxides

A single-domain GdBCO bulk superconductor is usually fabricated using a mixture of pre-reacted precursor powders (including GdBa2Cu3O7−δ and Gd2BaCuO5) by the top-seeded melt texture growth (TSMTG) process. However, the synthesis of pure-phase precursor powder by the solid-state sintering reaction can not only consume time for weeks but also prolong the fabrication process and can lead to a low-efficiency and high-cost process. In this paper, we reported the successful growth of single-domain GdBCO bulk superconductors by the top-seeded metallic oxide melt growth (TS-MOMG) process in which the raw materials of Gd2O3, BaO, and CuO, the three different metallic oxides, are just involved to fabricate the single-domain GdBCO bulk superconductors. After detailed investigations in the morphology, levitation force, trapped magnetic field, and critical temperature of the grown samples with different ratios, it was found that the simplified precursor-phase source can be used to fabricate the single-domain GdBCO bulk superconductors more efficiently, which can combine the crystal growth procedure and greatly economize the preparation cost and the time to the most extent.

A robust seeding technique for the growth of single grain (RE)BCO and (RE)BCO–Ag bulk superconductors

Bulk, single grains of RE–Ba–Cu–O [(RE)BCO] high temperature superconductors have significant potential for a wide range of applications, including trapped field magnets, energy storage flywheels, superconducting mixers and magnetic separators. One of the main challenges in the production of these materials by the so-called top seeded melt growth technique is the reliable seeding of large, single grains, which are required for high field applications. A chemically aggressive liquid phase comprising of BaCuO2 and CuO is generated during the single grain growth process, which comes into direct contact with the seed crystal either instantaneously or via infiltration through a buffer pellet, if employed in the process. This can cause either partial or complete melting of the seed, leading subsequently to growth failure. Here, the underlying mechanisms of seed crystal melting and the role of seed porosity in the single grain growth process are investigated. We identify seed porosity as a key limitation in the reliable and successful fabrication of large grain (RE)BCO bulk superconductors for the first time, and propose the use of Mg-doped NdBCO generic seeds fabricated via the infiltration growth technique to reduce the effects of seed porosity on the melt growth process. Finally, we demonstrate that the use of such seeds leads to better resistance to melting during the single grain growth process, and therefore to a more reliable fabrication technique.

Superconducting Performance, Structure, Microstructure, and Trapped Field of Top-Seeded Melt-Processed Bulk Y3Ba5Cu8Ox

The sintering temperature for the production of Y3Ba5Cu8O18 (Y-358) preform powders synthesized in sol-gel spontaneous combustion technique was optimized. A large single-grain bulk Y-358 crystal was fabricated employing a top-seeded melt-growth technique utilizing the optimally sintered preform powders (i.e., at 900 ∘C for 12 h). Structural, microstructural, elemental, and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscopy, and SQUID, respectively. The structural characterization indicated that the sample is highly textured in (00l) direction. The Y-358 phase fractions were estimated in both preform powders and bulk sample using Rietveld refinement. The onset of superconducting transition is observed at 92.5 K, and the curve is very sharp indicative of the high quality of the produced bulk sample. The field dependence of critical current density (Jc) was determined at 77 K, and the self-field Jc was found to be ∼26 kA/cm2. A magnetic field of 0.27 T was trapped by the sample at 77 K.

The successful incorporation of Ag into single grain, Y–Ba–Cu–O bulk superconductors

The use of RE-Ba–Cu–O [(RE)BCO] bulk superconductors, where RE = Y, Gd, Sm, in practical applications is, at least in part, limited by their mechanical properties and brittle nature, in particular. Alloying these materials with silver, however, produces a significant improvement in strength without any detrimental impact on their superconducting properties. Unfortunately, the top seeded melt growth technique, used routinely to process bulk (RE)BCO superconductors in the form of large, single grains required for practical applications, is complex and has a large number of inter-related variables, so the addition of silver increases the complexity of the growth process even further. This can make successful growth of this system extremely challenging. Here we report measurements of the growth rate of YBCO-Ag fabricated using a new growth technique consisting of continuous cooling and isothermal hold process. The resulting data form the basis of a model that has been used to derive suitable heating profiles for the successful single grain growth of YBCO-Ag bulk superconductors of up to 26 mm in diameter. The microstructure and distribution of silver within these samples have been studied in detail. The maximum trapped field at the top surface of the bulk YBCO-Ag samples has been found to be comparable to that of standard YBCO processed without Ag. The YBCO-Ag samples also exhibit a much more uniform trapped field profile compared to that of YBCO.

Synthesis and properties of YBa2Cu3O7-δ – Y2Ba4CuWO10.8 superconducting composites

YBa2Cu3O7-δ (YBCO) is a well-known high-temperature superconductor. However, its critical current density and thus maximum trapped magnetic field can be improved significantly by introducing the secondary phases (artificial pinning centers). In this contribution, we successfully prepared YBCO single-grain bulks with Y2Ba4CuWO10.8 phase serving as a source of pinning centers. This phase was prepared by solid-state reaction and further refined by milling. In the next step single-grain YBCO bulks with homogeneously distributed Y2Ba4CuWO10.8 were prepared by top-seeded melt growth. Precursors as well as the final product were characterized by XRD, SEM and EDS. The phase composition of YBCO bulks containing Y2Ba4CuWO10.8 was analyzed using Rietveld analysis. Thermal stability of YBCO bulk was studied by STA. Furthermore, PPMS was used to study electrical resistivity and critical current density. Bulk superconducting properties such as levitation force and trapped field ability were also measured.

Growth rate of YBCO-Ag superconducting single grains

The large scale use of (RE)Ba2Cu3O7 bulk superconductors, where RE=Y, Gd, Sm, is, in part, limited by the relatively poor mechanical properties of these inherently brittle ceramic materials. It is reported that alloying of (RE)Ba2Cu3O7 with silver enables a significant improvement in the mechanical strength of bulk, single grain samples without any detrimental effect on their superconducting properties. However, due to the complexity and number of inter-related variables involved in the top seeded melt growth (TSMG) process, the growth of large single grains is difficult and the addition of silver makes it even more difficult to achieve successful growth reliably. The key processing variables in the TSMG process include the times and temperatures of the stages within the heating profile, which can be derived from the growth rate during the growth process. To date, the growth rate of the YBa2Cu3O7-Ag system has not been reported in detail and it is this lacuna that we have sought to address. In this work we measure the growth rate of the YBCO-Ag system using a method based on continuous cooling and isothermal holding (CCIH). We have determined the growth rate by measuring the side length of the crystallised region for a number of samples for specified isothermal hold temperatures and periods. This has enabled the growth rate to be modelled and from this an optimized heating profile for the successful growth of YBCO-Ag single grains to be derived.

Melt growth of organic 4-(2-Phenylisopropyl) phenol single crystal and its structural, thermal, dielectric permittivity and optical properties

A nonlinear optical (NLO) organic crystal 4-(2-Phenylisopropyl) phenol has been grown by a top seeded melt growth technique. The melt growth kinetics of solid-liquid (molten) interface and facets formation in melt growth were studied. The melt grown crystal has the (001), (001¯),(110)(1¯1¯0),(1¯20),(12¯0),(2¯10) and(21¯0) different morphological face. The morphological characteristics of melt grown crystal helps to better infer the kinetic influence of melt and hone growth of organic material. The rhombohedral lattice cell parameters were measured by single crystal X-ray diffraction. 4-(2-Phenylisopropyl) phenol crystallizes in space group of R3¯. Thermal study shows that solid to liquid transition occurring at 350 K and decomposes at 597 K. The grown crystal was optically transparent in the wavelength range of 300–1100 nm. The low dielectric constant (9–11) was measured in the [001] of 4-(2-Phenylisopropyl) phenol crystal.

Structural and magnetic properties of the ring shaped 40 wt% Y211 added TSMG Y123 bulk superconductors welded by Ag2O added MPMG YBCO solder material

In this study, two 40% Y211+Y123 bulk superconductors named Y-1 and Y-2 were fabricated by cold top seeding-melt-growth (TSMG) method by using a Nd123 seed with Y2O3 buffer layer placed to bottom of the pellets. The samples were welded with 17 wt% Ag2O+Y123 bulk sample named Y-Ag using as a solder material with a lower decomposition temperature and is produced by melt-powder-melt-growth process (MPMG) with Y2O3 buffer layer. Small specimens were cut above, below and on welding regions of the welded sample and were named as Y-a, Y-b and Y-ab, respectively. The welded solder material and welded samples were studied with XRD, SEM structural analysis, resistivity and magnetization measurements. The welding region was mechanically durable and supported the critical current density (J c ) across the joints. The interface of the parent bulk surface and the epitaxially nucleated interfaces are very clean and no residual liquid phases or defects are observed. The onset (T c,onset ) and offset (T c,offset ) critical temperatures and upper critical fields (H c2 ) of the samples were evaluated from the magneto resistivity curves. Below the superconducting onset temperature of around 93 K, all samples exhibit sharp superconducting transition with their T c (R ≈ 0) of around 92 K at the 0 T magnetic field, showing that the welding process had no disruptive effect on T c . The H c2 (0) values were 175, 133 and 91 T for Y-a, Y-ab and Y-b respectively. The calculated J c values of Y-a, Y-b and Y-ab were 3.71, 3.38 and 3.08 kA/cm2, respectively, in 0 T field at 77 K. It was obtained that, the J c value of the welding region is the comparable to the welding bulks. As a result, we have succeeded in producing a strongly coupled superconducting YBa2Cu3O7−x joint by combining two bulk superconductors of TSMG Y123 by using a 17 wt% Ag2O added MPMG Y123 solder material.

Influence of annealing in oxygen and argon on the superconducting properties of Li-doped YBCO single-grain bulks

YBa2(Cu1-xLix)3O7-δ single-grain bulk superconductors with different Li concentrations were grown using the top-seeded melt growth process. Structural analysis of the samples and magnetisation measurements showed that substitution of the Cu atoms by the Li atoms took place in the YBa2Cu3O7-δ crystal lattice. This substitution was accompanied by the formation of effective pinning centres, which improved the pinning properties of the samples and increased the critical current density. Additional annealing and reannealing in oxygen and argon showed that the superconducting transition temperature displays substantially more suppression, when the Li-doped YBa2Cu3O7-δ samples were annealed in argon, that was associated with different distribution of the Li atoms between the CuO chains and the CuO2 planes in comparison to annealing in oxygen. Investigation of the critical current densities showed that the pinning properties of YBa2(Cu1-xLix)3O7-δ single-grain bulk superconductors did not depend on the arrangement of the Li atoms in the YBa2Cu3O7-δ crystal lattice. It was also observed that the crystal lattice parameters and the mean diameter of the non-superconducting Y2BaCuO5 particles systematically change with Li concentration.

A novel pre-sintering technique for the growth of Y–Ba–Cu–O superconducting single grains from raw metal oxides

Most established top seeded melt growth (TSMG) processes of bulk, single grain Y–Ba–Cu–O (YBCO) superconductors are performed using a mixture of pre-reacted precursor powders. Here we report the successful growth of large, single grain YBCO samples by TSMG with good superconducting properties from a simple precursor composition consisting of a sintered mixture of the raw oxides. The elimination of the requirement to synthesize precursor powders in a separate process prior to melt processing has the potential to reduce significantly the cost of bulk superconductors, which is essential for their commercial exploitation. The growth morphology, microstructure, trapped magnetic field and critical current density, Jc, at different positions within the sample and maximum levitation force of the YBCO single grains fabricated by this process are reported. Measurements of the superconducting properties show that the trapped filed can reach 0.45 T and that a zero field Jc of 2.5 × 104 A cm−2 can be achieved in these samples. These values are comparable to those observed in samples fabricated using pre-reacted, high purity commercial oxide precursor powders. The experimental results are discussed and the possibility of further improving the melt process using raw oxides is outlined.