Jc Values Research Articles

Универсальность поведения гистерезиса магнитосопротивления и его температурной эволюции для гранулярных высокотемпературных сверхпроводников Y-Ba-Cu-O

The work is devoted to the establishment of regularities in the behavior of the magnetoresistance hysteresis R(H) of granular high-temperature superconductors (HTS) of the yttrium system. We carried out a comparative study of the magnetotransport properties of granular HTSC samples, which have (i) approximately the same magnetic properties and temperatures of the onset of the superconducting transition (90.5–93.5 K, which characterizes HTS grains) and (ii) different values of the transport critical current JC (which characterizes the intergrain boundaries). Despite the significant scatter in the JC values (more than an order of magnitude) of the three samples studied, a universal behavior of the magnetoresistance hysteresis was found, apparently inherent in all granular Y-Ba-Cu-O. The R(H) hysteresis is very wide, and in a sufficiently large interval of the external field, the dependence of the hysteresis width of the magnetoresistance H on the field Hdec (external field H = Hdec for a decreasing hysteresis branch) is close to a linear function: H ≈ Hdec. This behavior is observed for the entire temperature range of realization of the superconducting state (the studies were carried out at temperatures of 77–88 K and 4.2 K). The explanation of the obtained result is based on the concept of consideration the effective field in the intergrain boundaries. This effective field is the superposition of the external field and the field induced by the magnetic moments of the grains. The field induced by the grains, in turn, is significantly enhanced in the region of intergrain boundaries due to the effect of the magnetic flux compression (the length of the intergrain boundaries is several orders of magnitude smaller than the size of the HTS grains). The above is confirmed from the analysis of the R(H) hysteresis for a composite HTS sample based on Y-Ba-Cu-O and CuO, in which the length of the intergranular boundaries is purposefully increased, as a result, the effect of the flux compression is less pronounced, and the hysteresis R(H) narrows.

Performance of ferritic steel 16MnDR using improved local fracture criterion

Based on the finite element analysis and fracture toughness test data, this paper verifies the improved Ritchie-Knott-Rice (RKR) local failure criterion using 16MnDR ferritic steel for cryogenic pressure vessels. This criterion's applicability to 16MnDR was verified to verify fracture toughness's different influence factors in the ductile-to-brittle transition temperature (DBTT) region, such as specimen thickness (TST) and temperature. The results indicate that the (4δt, σ22c) criterion applies to 16MnDR steel and effectively transfers the minimum Jc value between samples of different temperatures and thickness.

Investigation of the physical properties of (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ impregnated with mono cobalt(II)-substituted Undecatungstosilicate Nanoparticles

A series of (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ superconducting samples impregnated with different percentage additions of potassium salt {CoSiW11}x nanoparticles (x = 0.00, 0.01, 0.02, 0.04, 0.06, 0.08 and 0.12 wt.%) were prepared using a single-step solid-state reaction technique at ambient pressure. These samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) to study their structures, construction of the synthesized samples and elemental composition, respectively. XRD studies indicate that the tetragonal structure of (Cu0.5Tl0.5)-1223 phase has not changed by the addition of {CoSiW11} nanoparticles the same as for the values of lattice parameters a and c, where they show a non-remarkable change. The relative volume fraction of (CuTl)-1223 phase record a maximum value for x = 0.02 wt.%. The formation of (CuTl)-1223 phase matches the presence of rectangular-shaped plates seen in SEM images. The enhancement of these plates after the addition of {CoSiW11} nanoparticles up to x = 0.02 wt.% agreed with the measurements of relative volume fraction. The mass percentage of all elements was measured using the EDX technique, which shows the distribution composition of both superconductor and nanoparticle compounds. Vibrational mode analyses of oxygen were accomplished via Fourier transform infrared (FTIR) spectroscopy in (CuTl)-1223 phase impregnated with {CoSiW11} nanoparticles. The Oδ oxygen modes observed are almost unaltered while the other oxygen modes of planar CuO2 are slightly softened and hardened. Superconducting transition temperature (Tc) and critical current density (Jc) were determined from the electrical resistivity and I–V measurements, respectively. The results indicate an increase in the Tc values from 125 K for the pure sample to 132 K for x = 0.02 wt.% impregnated samples, while a decrease in the Jc values is observed upon increasing ‘x’ value from x = 0.00 up to 0.12 wt.%. The suppression of these electrical superconducting parameters for x > 0.02 wt.% may be due to an increase of weak links' connectivity among the grain boundaries and growth of impurity phases that affect the formation of (CuTl)-1223 superconductor phase. The fluctuation-induced conductivity (FIC) analysis has been done in the light of the Aslamasov–Larkin (AL) theory to study the fluctuation conductivity Δσ above Tc as a function of reduced temperature for (CoSiW11)x/(CuTl)-1223 superconductor. The results show four non-identical fluctuation regions that are short-wave (Sw), two-dimensional (2D), three-dimensional (3D) and critical (Cr). The zero-temperature coherence length ( $${\xi }_{c}(0)$$ ), the effective layer thickness of the two-dimensional system (d), inter-layer coupling (I), Fermi velocity (vF) and Fermi energy (EF) were evaluated as a function of ‘x’ addition from FIC analysis of the samples and then correlated to the superconductivity order parameters. The superconducting parameters were increased upon the addition of {CoSiW11} nanoparticles.

Investigation of the crystallization process of CSD-ErBCO on IBAD-substrate via DSD approach

REBa2Cu3O7-δ (REBCO, RE: rare earth, such as Y and Gd) compounds have been extensively studied as a superconducting layer in coated conductors. Although ErBCO potentially has better superconducting properties than YBCO and GdBCO, little research has been made on it, especially in chemical solution deposition (CSD). In this work, ErBCO films were deposited on IBAD (ion-beam-assisted-deposition) substrates by CSD with low-fluorine solutions. The crystallization process was optimized to achieve the highest self-field critical current density (Jc) at 77 K. Commonly, for the investigation of a CSD process involving numerous process factors, one factor is changed keeping the others constant, requiring much time and cost. For more efficient investigation, this study adopted a novel design-of-experiment technique, definitive screening design (DSD), for the first time in CSD process. Two different types of solutions containing Er-propionate or Er-acetate were used to make two types of samples, Er-P and Er-A, respectively. Within the investigated range, we found that crystallization temperature, dew point, and oxygen partial pressure play a key role in Er-P, while the former two factors are significant for Er-A. DSD revealed these significant factors among six process factors with only 14 trials. Moreover, the DSD approach allowed us to create models that predict Jc accurately. These models revealed the optimum conditions giving the highest Jc values of 3.6 MA/cm2 for Er-P and 3.0 MA/cm2 for Er-A. These results indicate that DSD is an attractive approach to optimize CSD process.

Excess Conductivity Analysis of Polycrystalline FeSe Samples with the Addition of Ag.

Bulk FeSe superconductors of the iron-based (IBS) “11” family containing various additions of silver were thoroughly investigated concerning the microstructure using optical microscopy and electron microscopy (TEM and SEM). The measurements of electrical resistivity were performed through the four-point technique in the temperature interval 2–150 K. The Aslamazov–Larkin model was employed to analyze the fluctuation-induced conductivity (FIC) in all acquired measurements. In all studied products, we found that the FIC curves consist of five different regimes of fluctuation, viz. critical region (CR), three-dimensional (3D), two-dimensional (2D), one-dimensional (1D), and shortwave fluctuation (SWF) regimes. The critical current density (), the lower and upper critical magnetic fields ( and ), the coherence length along the c-axis at zero-temperature ((0)), and further parameters were assessed with regards to the silver amount within the products. The analyses discloses a diminution in the resistivity and a great reduction in (0) with Ag addition. The optimal silver doping amount is achieved for 7 wt.%, which yields the best superconducting transition and the greatest value.

Flux pinning mechanisms of (YBa2Cu3Oy-d)1−x/(Dy2O3)x superconductors (x=0.1 and 0.5 wt%)

Polycrystalline (YBa2Cu3Oy-d)1−x/(Dy2O3)x superconductor samples were produced through the solid-state reaction route and by adding amounts of x = 0.1 and 0.5 wt% of Dy2O3 nanoparticles (NP-Dy2O3 with a size of about 10 nm) during the second stage of heat treatment. The structural, microstructural, critical current density and pinning properties were investigated using x-ray diffraction, scanning electron microscope, and DC magnetization at various temperatures ranging from 77 down to 10 K and under an applied magnetic field varying between −6 and +6 Tesla. Both samples crystallize in the orthorhombic structure. It was found that the Dy2O3 nanoparticles reside in the grain boundaries. Although the sample with 0.5 wt% NP-Dy2O3 is characterized by a low zero resistive temperature of about 78 K that is close to the useful temperature for technological applications, it showed the highest Jc values and the excellent flux pinning capacity. The addition of an appropriate amount of NP-Dy2O3 up to 0.5 wt% extends the single bundle pinning regime and retards the liquid vortex regime.

Enhanced critical current density in Nb3Al superconductor by optimizing mechanical alloying and subsequent sintering process

The critical current density (Jc) is one of the most important properties for the practical application of Nb3Al superconductors. In this work, Nb3Al bulk superconductors were synthesized by mechanical alloying (MA) and subsequent sintering process. And its Jc performance is improved through optimizing the process parameters including ball milling time, sintering temperature and holding time. The results show that the optimal ball milling time to acquire high Jc performance was 20 h. Excessive ball milling worsened Nb3Al's Jc performance because some impurities were introduced into sintered sample. The holding time during sintering process mainly affected the grain size of Nb3Al. Some fine grains coalesce into larger ones after long time sintering. Besides, the sintering temperature and the holding time were all of significance to the grain connectivity in Nb3Al. Higher sintering temperature and longer holding time made a better grain connectivity. The highest Jc value of Nb3Al bulk was 2.5 × 104 A/cm2 (4.2 K, 6 T) with the sintering condition of 850 °C for 5 h. Our work raises some valuable discussions for the following studies on Nb3Al superconductor.

Superconducting and levitation force characterisation of pyrene added MgB2 bulk superconductors

This research presents the influence of pyrene (C16H10) addition (0, 2, 4, 6, 8, 10 wt%) on the superconducting properties of bulk MgB2. For C16H10 added MgB2 samples, a shrinkage in a-lattice parameters was determined, whereas c-lattice parameters remained practically unchanged. The (110) peak observed at 2θ ≈ 59.9◦ slightly shifted to higher angles, the lattice strain increased and the crystallite size reduced after C16H10 addition. By virtue of induced stronger pinning force, the in-field critical current density (Jc) increased after C16H10 addition. The Jc value at 20 K and 4 T was obtained about two times higher (8.54 × 103 A/cm2) for 4 wt% C16H10 added MgB2 sample than that of the pure one. In addition, the variation of levitation force characteristic of MgB2 with increasing C16H10 content was determined at 20, 25 and 30 K. The best vertical levitation force performance in zero-field-cooled regime was obtained as 7.09 N/g at 20 K for 4 wt% C16H10 added MgB2 sample with 13 mm in diameter.

On a New Number Equation Incorporating Both Temperature and Applied Magnetic Field and Its Application to MgB2

Guided by recent studies that point to the pivotal role played by the Fermi energy (EF) in determining the properties of high-temperature superconductors, we have been following a course where the critical temperature, gap(s), and the temperature T- and the applied magnetic field H-dependent critical current density jc (T, H) are addressed in a unified, EF-incorporated framework. Needed in such an approach is an equation for the number density ns (T, H) which is a constituent of jc (T, H). This equation is derived here by applying the field-theoretic Landau quantization prescription to ns (T, H = 0). As an application of the new equation, we also deal herein with a few empirical values of jc (T, H) of MgB2 and show that the corresponding ns (T, H) values lead to bounds on the effective mass of the charge carriers, the Fermi velocity, and the critical velocity.

Simultaneous achievement of high Jc and suppressed Jc anisotropy by hybrid pinning in YBa2Cu3O7 three-phase-nanocomposite film

Nanoscale pinning centers are introduced into YBa2Cu3O7 (YBCO) films and tapes to improve vortex pinning and critical current density (Jc) for coated conductor application. While pinning with a single type of pinning center has been mainly investigated, hybrid pinning with multiple types of pinning center is expected to be more promising for simultaneously achieving high Jc values and suppressing Jc anisotropy. In the present study, a three-phase-nanocomposite film consisting of an YBCO matrix, BaHfO3 nanorods and Y-O nanoparticles was fabricated. A global pinning force maximum (Fp,max, where Fp = JcB) of 1.57 TN m−3 at 4.2 K, which is as high as the record level of Fp,max, was achieved by the hybrid pinning of BaHfO3 nanorods and Y-O nanoparticles. Furthermore, the hybrid pinning improved the angular dependence of Jc. The pinning contribution from nanoparticles increased with lowering temperature, which can explain the high Jc at low temperature. Thus, the present study successfully demonstrates a highly effective structure that can simultaneously achieve suppressed Jc anisotropy and a record level of Jc.

Developments of (Ba,Na)Fe2As2 and CaKFe4As4 HIP round wires

With excellent superconducting properties such as high Tc, large Hc2, small anisotropy, and large Jc, developments of superconducting wires and tapes of iron-based superconductors (IBSs) have been undertaken with promising results. So far, K-doped 122-type IBSs have been mainly developed for such purposes. Here, efforts to fabricate Na-doped 122-type IBS, (Ba,Na)Fe2As2, are presented. With the help of hot isostatic pressing (HIP) process, excellent Jc characteristics of up to 44 kA cm−2 at 4.2 K under 100 kOe have been achieved. Detailed characterizations of (Ba,Na)Fe2As2 HIP round wire are presented. On the other hand, discoveries of new IBSs continue, with CaKFe4As4 as one of recent examples. CaKFe4As4 belongs to a new family of IBSs with 1144 structure, where Ca and K occupy the Ba site in BaFe2As2 alternately along the c-axis. Studies on CaKFe4As4 single crystals have demonstrated moderately large Jc with peculiar anisotropic properties related to the presence of novel planar defects. We have also fabricated HIP round wires of CaKFe4As4, and reported their basic characterizations. Despite the instability of CaKFe4As4 at low temperatures, Jc values at 4.2 K close to 100 kA cm−2 at self-field and 7.6 kA cm−2 at 100 kOe are achieved. Attempts to introduce defects into CaKFe4As4 single crystals, chemically by Co substitution and physically by proton irradiation, are attempted, and the effects are compared. Attempts to fabricate Co-doped CaKFe4As4 HIP round wires with limited success are also reported.

Structural, Magnetic, and Electrical Properties of Bi1.6Pb0.4Sr2Ca2Cu3O10+x Superconductor Prepared by Different Techniques

In present work, we investigated the structural, magnetic, and electrical properties of Bi1.6Pb0.4Sr2Ca2Cu3O10+x superconductor prepared by using four different techniques: (i) solid-state (A), (ii) sol-gel (B), (iii) chemical wet (C), and (iv) melt-quench (D). From x-ray diffraction (XRD) and transmission electron microscopy (TEM) results, it is observed that the sintering process does not influence final crystallite size of compounds, but final crystallite sizes of the compounds were nearly the same after sintering process, while initial crystallite sizes were found to be different after the preparation process. From the XRD results, it is seen that the main phase in the compound is low-Tc Bi-(2212) phase and all samples contain a small amount of high-Tc Bi-(2223) phase. From scanning electron microscopy (SEM), two different types of surface crystallization of the compounds have been observed. The low-temperature resistivity, R(T), measurements show that all compounds have low zero resistivity, Tc,offset, value. Samples A, B, and C show the high-Tc and low-Tc transition at 110 and 75 K, respectively, while sample D displays only low-Tc transition at 75 K. These results have been supported by magnetization versus temperature measurement, M(T). In order to calculate critical current, Jc, values for the samples, magnetic hysteresis curves were taken at temperatures 10, 20, 30, 40, 50, and 60 K between the fields of ± 9 T. The hysteresis and the Jc calculation results show that sample D, when compared with other samples, has the best superconducting properties and has the highest Jc value. The best superconductivity properties between the studied samples have been obtained for sample A, while the best magnetic properties and the highest Jc value have been observed for sample D. According to the results obtained in this study, the structural and superconducting properties change with sample preparation method.

Improved biaxial texture of tri-layer YBCO/CaTiO3/YBCO films using an all chemical solution deposition method

The chemical solution deposition (CSD) is one of the most appealing routes for the growth of high-quality YBa2Cu3O7-δ (YBCO) films due to its advantages of low cost and high efficiency. However, as with other preparation methods such as pulsed laser deposition (PLD), the critical current densities (JC) of YBCO films prepared by the CSD method also dramatically decrease with increasing film thickness, which is known as thickness effect. In this paper, the tri-layer YBCO/CTO/YBCO thick films were deposited on buffered Hastelloy C276 tapes by using a dip coater based on all CSD method. By means of the introduction of the CTO interlayer, the JC reduction with increasing film thickness was inhibited, arising from the improvement of the biaxial texture in the tri-layer thick film. The JC value (77 K, self-field) of the tri-layer film was around 3.3 MA/cm2. The texture improvement was mainly ascribed to the interface levelling through the deposition of the CTO interlayer which is a template with good biaxial texture for the epitaxial growth of YBCO film.

The effect of the sintering process on Ag–added FeSe0.94 superconducting wire

We investigated the effect of different sintering processes on Ag–added FeSe0.94 superconducting wires. After applying different sintering procedures, we successfully obtained zero resistivity, at 350 °C for 100 h and at 700 °C for 1 h, in Ag–added FeSe0.94 superconducting wire produced using the ex-situ powder-in-tube method. The crystal structure of both wires is mainly composed of the tetragonal β–FeSe phase. Ag does not react with selenium, and it can be incorporated into the crystal structure. The transport Jc value of these wires is calculated to be 24.4, and 38 A cm−2 at 4.2 K in a self-field, respectively. The low current densities of the wires are attributed to the low core–density and the presence of porosity. The upper critical field is estimated to be 16.2 and 14.6 T from Werthamer–Helfand–Hohenberg theory, respectively.

High homogeneity 10 cm long BaTiO3-doped YBa2Cu3O7-δ films by the trifluoroacetate metal-organic deposition process

The trifluoroacetate metal-organic deposition (TFA-MOD) is one of the most appealing routes for the growth of high-quality YBa2Cu3O7-δ (YBCO) coated conductors (CCs) due to its advantages of low cost and high efficiency. However, the puzzle of the inhomogeneities in microstructures and superconducting properties of YBCO CCs prepared based on the TFA-MOD route remain still a challenge. In this paper, 10 cm long YBCO films were prepared under different low-pressure conditions. These YBCO films were deposited on buffered Hastelloy C276 tapes using a dip coater. The effect of different ambient pressures on the microstructure and critical current density of YBCO films was investigated. High critical current density (JC) YBCO coated conductors with good homogeneity were obtained. The JC values (77 K, self-field) at different positions along the length direction of YBCO coated conductor were around 3.5–4 MA/cm2. The results showed that only under a suitable pressure the homogeneities of the microstructure and critical current density along the length direction of coated conductor can be greatly improved. The improvement was mainly ascribed to good texture and the absence of impurity phases BaF2 and Ba4Y2O7 in the films.

Synthesis routes to eliminate oxide impurity segregation and their influence on intergrain connectivity in K-doped BaFe2As2 polycrystalline bulks

The poor reproducibility of intergrain critical current density Jc in Fe-based superconductors is often believed to result from uncontrolled grain boundary (GB) connectivity degraded by extrinsic factors such as the local or global impurity concentration or GB porosity or cracks. Earlier we found that Ba and K can appear as oxide impurities at GBs, along with GB-wetting FeAs. In this study, we evaluated how the sample preparation environment and purity of the starting materials influence the polycrystalline Jc in K-doped BaFe2As2 (Ba122) bulks. Using a high-performance glovebox, the oxygen and water levels were significantly reduced, eliminating traces of FeAs. Oxide impurities and Ba (or K) segregation associated with oxygen in the starting materials were significantly reduced by using high purity starting materials. This combination essentially doubled the best Jc(4.2 K) values to 2.3 × 105 at self-field and 1.6 × 104A cm−2 at 10 T and analytical scanning transmission electron microscopy showed no GB or O segregation in the best samples, but did show dark Z-contrast and distinct nanoscale porosity. Our work shows that an inert synthesis environment and high purity K and Ba do reduce current-blocking oxygen impurity and GB impurity phases, allowing deeper exploration of the role of extrinsic and intrinsic GB blocking effects in controlling the Jc of polycrystalline Ba122.

Reduced sintering temperature in ex situ processed MgB2 tapes using filling powders with Sn addition

Ex situ processed tapes using ball milled MgB2 powders with Sn addition were sintered at various temperatures. Sn addition causes the formation of some amorphous or poor crystalline phase in the as-milled powders and reduces the optimal sintering temperature (Tsin), at which best performance in transport critical current density (Jc) at 4.2 K in 10 T is obtained for the tapes, to about 600 °C. This temperature is lower than that by about 100 °C for the tapes using the milled powders without Sn addition. However, Tsin reduction brings about the decrease of critical temperature (Tc) as well. Nevertheless the addition of small amount of Sn does not cause Jc deterioration at all and the Jc value at 4.2 K and 10 T is around 200 A/mm2. Although the Jc property degrades with further decreasing the Tsin, the corresponding value is still 100 A/mm2 when sintered at 500 °C. The Jc curves as a function of Tsin just shift to lower temperatures by about 100 °C by Sn addition. The anisotropy of the transport Jc property with respect to the applied magnetic field direction is negligible, which is independent of Sn addition.

Enhancement of critical current density in helium ion irradiated Ba(Fe, Co)2As2 thin films

The effect of 600 keV He+ ion irradiation on the temperature and magnetic field dependence of the critical current density JC in high quality BaFe1.84Co0.16As2 (Co-doped Ba122 type) thin films is investigated. The films are prepared by pulsed-laser-deposition (PLD) on CaF2 (00 ) substrates. The irradiation dosages are varied between 1 × 1013 and 1 × 1016 cm−2. Upon irradiation, the superconducting transition temperature TC drops slightly from 25 K for the unirradiated sample to about 20 K for the sample with the highest irradiation level. The JC values of the thin film samples are calculated by using the Bean critical state model. The results showed that JC could be enhanced substantially. The maximum JC value at 4.5 K temperature is enhanced up to 2.4 MA cm−2 under 1 T field. The analysis of pinning force dependence on magnetic field shows that the pinning behavior is not changed in the irradiated samples, suggesting more pinning centers of similar nature to those of presented in the unirradiated samples are introduced by the irradiation process. The results indicate that the irradiation of light element ions He+ with relatively low energy could increase the critical current density in iron based superconductors.

Effect of annealing conditions on the superconducting properties of nano-sized metallic Au-added Bi1.8Sr2Au0.2Ca1.1Cu2.1Oy (Bi-2212) ceramics

In this study, the effects of annealing process on the phase formation and electrical and magnetic properties of nano-sized metallic Au-added Bi-2212 ceramics have been investigated. The Bi1.8Sr2Au0.2Ca1.1Cu2.1Oy including x = 0.2 Au content as starting composition was chosen due to the improved transport properties in the Bi-2212 system, as known in the literature. The samples for the post-annealing technique were exposed at different dwell times (10 m, 30 m, 1 h, and 2.5 h) at a fixed temperature of 870 °C after the application of normal heat treatment of 850 °C for 120 h. The XRD diagrams clearly indicate that a significant part of the phases in all the samples belongs to Bi-2212 phase. SEM results show that all the samples have randomly oriented grain forms as the main characteristic of applied solid-state method. In all cases, the post-annealed samples showed better superconducting properties of Bi-2212 phase, indicating that the increases in the dwell time positively affect its granular polycrystalline character such as inter-connectivity of the grains, the nucleation, and growth of the Bi-2212 phase. Moreover, the sample with dwell time of 2.5 h at 870 °C reveals significant enhancement in the M–H loops compared to the sample with less dwell time, despite the fact that the Bi-2212 phase can easily decompose into secondary phases such as Cu-free and Bi-free due to thermodynamic instabilities of Bi-2212 at temperatures above 860 °C. Finally, the intragranular critical current density values (Jc) have been obtained by using the data from M-H measurements according to the critical Bean model. It has been found that the Jc value (16.5 × 104 A/cm2 in 0.15 T at 15 K) of the sample in the dwell time of 2.5 h at 870 °C is higher than that of the sample (13.4 × 104 A/cm2 in 0.15 T at 10 K) with the same starting composition reported in the literature.

Interplay between cold densification and malic acid addition (C4H6O5) for the fabrication of near-isotropic MgB2 conductors for magnet application

Abstract The effect of cold high pressure densification (CHPD) on anisotropy of the critical current density (Jc) in « in situ » single core binary and alloyed MgB2 tapes has been determined as a function of temperatures at 4.2 K, 20 K and 25 K as well as at applied magnetic fields up to 19 T. The study includes binary and C4H6O5 (malic acid) doped MgB2 tapes before and after CHPD. It is remarkable that the CHPD process not only improved the Jc values, in particular at the higher magnetic fields, but also decreased the anisotropy ratio, Γ = Jc///Jc┴. In binary MgB2 tapes, the anisotropy factor Γ increases with higher aspect ratios, even after applying CHPD. In malic acid (C4H6O5) doped tapes, however, the application of CHPD leads only to small enhancements of Γ, even for higher aspect ratios. This is attributed to the higher carbon content in the MgB2 filaments, which in turn is a consequence of the reduced chemical reaction path in the densified filaments. At all applied field values, it was found that CHPD processed C4H6O5 doped tapes exhibit an almost isotropic behavior. This constitutes an advantage in view of industrial magnet applications using wires with square or slightly rectangular configuration.