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Razvojem prometne infrastrukture, posebice cestovne, te porast broja vozila znatno utječe na povećanje razine buke. Zaštita od prometne buke danas je prioritet u zemljama EU. Uobičajeni načini zaštite od buke uz prometnice je primjena barijera za zaštitu od buke. U radu se prikazuje zaštita od buke primjenom apsorbirajućih betonskih barijera. Apsorbirajući sloj betonskih barijere se uobičajeno izrađuje od laganog betona s ekspandiranom glinom ili s drvenim vlaknima. S ciljem pronalaženja alternativnog materijala za izradu apsorpcijskog sloja betonskih barijera, ali pri tome vodeći računa o održivom razvoju Građevinski fakultet Sveučilišta u Zagrebu razvio je betonske barijere za zaštitu od buke tipa RUCONBAR (Rubberized Concrete Noise Barriers) čiji je apsorpcijski sloj izveden laganim betonom s dodatkom gumenih granula dobivenih reciklažom otpadnih guma. Barijere RUCONBAR u strukturi svojeg apsorbirajućeg sloja sadrže 40 % gumenog granulata dobivenog recikliranjem otpadnih guma i kao takav predstavlja inovativno i ekološko rješenje u proizvodnji barijera za zaštitu od buke.

Electrical resistivity and critical current density of undoped and doped with short multiwalled carbon nanotubes (SMW_CNT) Fe-sheathed wires and tapes annealed at 900°C and 1000°C respectively, have been investigated in the temperature range 2-40K and in magnetic field B ~ 16T. The amount of dopand was chosen to correspond to stoichiometric formula MgB1.8C0.2. Doping via partial substitution of boron with carbon in MgB2 decreases the superconducting transition temperature Tc, but increases the low temperature upper critical field Hc2, due to alloying effects in two gap MgB2 superconductor [1] and these effects are more pronounced in sample annealed at higher temperature. The actual amount of substitution of boron with carbon was deduced from the decrease of Tc upon doping. At the same time, the inhomogeneous doping, nanoprecipitates formed during annealing and the remnants of SMW-CNT enhance the pinning of vortices in doped samples at lower temperatures (T

Rad prikazuje rezultate ispitivanja mjesta zrakopropusnosti obiteljske kuće korištenjem metode IC termografije.

Dopiranje nanočesticama poboljšava elektromagnetska svojstva (kritičnu struju u magnetskom polju, J_c(B), volumnu silu zapinjanja, F_p=J_cB, karakteristična polja, B_c2 i B_irr, itd.) supravodiča MgB_2, što ga uz višu temperaturu supravodljivih prijelaza, T_c=39K i nižu cijenu sastojaka čini mogućom zamjenom danas korištenih supravodiča NbTi i Nb_3Sn. Sažeto ćemo prikazati novije rezultate dobivene nanodopiranjem MgB_2, te razmotriti moguće mehanizme postignutih poboljšanja elektromagnetskih svojstava (ES). Razmotrit ćemo i perspektive daljnjeg poboljšanja ES MgB_2 kao i probleme koje pritom treba riješiti.

Transport critical current densities J_c and irreversibility fields B_irr of undoped and nanoparticle doped (10 wt% SiC) Fe-sheathed MgB_2 wires were measured from 2 to 40K in magnetic field B

Irreversibility fields Birr and critical current densities Jc of undoped and doped (10 wt.% SiC) MgB2/Cu tapes and MgB2/Fe wires were measured from 2 K up to 38 K in magnetic field B1 T, Birr(T) variation for all samples is similar, but Birr of MgB2/Fe is higher than that of corresponding MgB2/Cu tapes. However, the enhancement of Birr upon doping, Birr(dop.)/Birr(undop.)=1.4 is the same for both types of samples indicating the same pinning mechanism. Birr of doped MgB2/Fe wire reaches that of optimised NbTi wires (10 T, 4.2 K) already at 20 K and extrapolates to 21 T at 4.2 K (close to that of Nb3Sn). In spite of low core density (~1.2 g/cm3) Jc of doped MgB2/Fe wire is high and decreases little with magnetic field: Jc(4.2 K)=19 kA/cm2 in B=13 T which yields FP=JcB=2.5 GN/m3. Since Jc and Jc-B variation in our samples is limited by core porosity and defects (cracks and voids), the Jc and FP values for more dense and homogeneous SiC doped samples are probably several times larger.

The influence of surface fields Hp (generated with either direct or alternating core-current) on soft magnetic properties of amorphous and nanocrystalline Fe73.5Cu1Nb3Si15.5B7 ribbon has been studied. While in amorphous ribbon the coercive field Hc decreases with Hp, in the same optimally annealed ribbon (Hc = 1.3 A/m, Mm ≈ Ms) Hc increases with Hp and the hysteresis loss E decreases with Hp for all explored types of Hp (static and dynamic with different phases with respect to that of the magnetizing field H). The unexpected increase of Hc in nanocrystalline ribbon is associated to the influence of Hp on the surface and main (inner) domain structure. The model is developed which takes into account this interaction and explains all experimental results. The probable adverse effect of the external fields with configurations similar to those of Hp on the performance of such ribbons is briefly discussed and some procedures which can prevent these effects are proposed., Proučavali smo utjecaj površinskih polja Hp (proizvedenih stalnom ili izmjeničnom strujom sredice) na meka magnetska svojstva amorfne i nanokristalinične trake Fe73.5Cu1Nb3Si15.5B7. Dok se koercitivno polje Hc u amorfonj traci smanjuje s Hp, u toj traci nakon najpovoljnijeg opuštanja (Hc = 1.3 A/m, Mm ≈ Ms) Hc raste s Hp, a gubici E zbog histerezne petlje smanjuju se s Hp za različita polja Hp (statičko, i dinamičko s različitim fazama u odnosu na magnetizirajuće polje H). Neočekivan porast Hc u nanokristalnoj traci povezuje se s utjecajem Hp na površinsku i osnovnu (unutarnju) domensku strukturu. Razvili smo model koji uključuje to međudjelovanje i objašnjava sve eksperimentalne rezultate. Raspravljamo moguće nepovoljne utjecaje vanjskih polja slične konfiguracije kao Hp na svojstva tih traka i predlažemo načine spriječavanja tih utjecaja.

A systematic study of the parameters (irreversibility field Birr, critical current density, Jc) associated with flux pinning in nanoparticle doped (Si, SiC, average size 50 nm) powder-in-tube processed MgB2/Cu composite tapes has been carried out. Birr and Jc of undoped and doped (5 and 10 wt.%) tapes were measured in the temperature range 4-38 K and in magnetic fields up to 16 T. Birr(T) of doped tapes shows a change in slope around characteristic field B_fi which increases with nanoparticle content and also depends on their type. This indicates matching effect in flux pinning, probably associated with Mg2Si nanoprecipitates (~10 nm) formed during heat treatment. The flux pinning enhancement factor Birr(doped)/Birr(undoped), was the highest around the matching field B_fi (the field at which the areal density of precipitates matches that of flux lines) but remained high ~1.5 even for Birr>>B_fi (low temperatures). This feature contrasts sharply with matching field effects in high temperature superconductors containing columnar defects (where the enhancement is confined to fields

Irreversibility fields Birr and critical current densities Jc of undoped and doped (10 wt.% SiC) MgB2/Cu tapes and MgB2/Fe wires were measured from 2 K up to 38 K in magnetic field B=1 T, Birr(T) variation for all samples is similar, but Birr of MgB2/Fe is higher than that of corresponding MgB2/Cu tapes. However, the enhancement of Birr upon doping, Birr(dop.)/Birr(undop.)~1.4 is the same for both types of samples indicating the same pinning mechanism. Birr of doped MgB2/Fe wire reaches that of optimised NbTi wires (10 T, 4.2 K) already at 20 K and extrapolates to 21 T at 4.2 K (close to that of Nb3Sn). In spite of low core density (~1.2 g/cm3) Jc of doped MgB2/Fe wire is high and decreases little with magnetic field: Jc(4.2 K)=19 kA/cm2 in B=13 T which yields FP=JcB=2.5 GN/m3. Since Jc and Jc-B variation in our samples is limited by core porosity and defects (cracks and voids), the Jc and FP values for more dense and homogeneous SiC doped samples are probably several times larger.

The influence of surface fields Hp (generated with either direct or alternating core-current) on soft magnetic properties of amorphous and nanocrystalline Fe73.5Cu1Nb3Si15.5B7 ribbon has been studied. While in amorphous ribbon the coercive field Hc decreases with Hp, in the same optimally annealed ribbon (Hc = 1.3 A/m, Mm  Ms) Hc increases with Hp and the hysteresis loss E decreases with Hp for all explored types of Hp (static and dynamic with different phases in respect to that of the magnetizing field H). The unexpected increase of Hc in nanocrystalline ribbon is associated to the influence of Hp on the surface and main (inner) domain structure. The model is developed which takes into account this interaction and explains all the experimental results. The probable adverse effect of the external fields with configurations similar to those of Hp on the performance of such ribbons is briefly discussed and some procedures which can prevent these effects are proposed.

The irreversibility fields Birr and critical current densities Jc of undoped and Si and SiC nanoparticle doped (5, 10 and 20 wt.%) MgB2 tapes were measured in the temperature (T) range 2-38 K and in magnetic fields B>Bcr (low temperatures). The variations of Jc and the pinning force density Fp=JcB with B and T support the above findings.

A systematic analysis of the parameters associated with vortex pinning in novel superconductors containing nano-scale strong isotropic pinning centres (such as U/n processed Bi2223/Ag tapes and nanoparticle added MgB2) has been carried out. Although the systems studied are very different as regards their structures, types of nano-scale defects and vortices, their pinning parameters (irreversibility fields and the fields for the maximum volume pinning force) show distinct common features. In particular, for moderate defect densities nφ, in all these systems the enhancement of the pinning parameters in nanostructured state is approximately linear in nφ over sizable field and temperature windows. Accordingly, these systems exhibit a kind of matching effects with the effective matching field Bφ, correlated with the areal density of defects. The field Bφ forms a natural field scale for the vortex pinning phenomena in such systems. However, at fields far from Bφ, an interplay of different pinning mechanisms sets in. The impact of these results for the future enhancement of the flux pinning and critical currents in nanostructured Bi2223 and MgB2 superconductors is briefly discussed., Predstavljamo sustavnu analizu parametara zapinjanja magnetskih vrtloga u novim supravodičima koji sadrže jake izotropne nanoskopske centre zapinjanja kao što su Bi2223/Ag trake obrađene sa U/n i MgB2 punjen nanočesticama silicija. Iako su ti materijali vrlo različiti u pogledu kristalne strukture, prirode vrtloga i nanoskopskih defekata, njihovi parametri zapinjanja vrtloga (ireverzibilna polja i polja maksimalne volumne sile zapinjanja) pokazuju izrazito slična svojstva. Npr., u tim je materijalima pojačanje zapinjanja vrtloga pri umjerenim gustoćama defekata nφ približno linearno s nφ u širokom području temperatura i magnetskih polja. Ukratko, ti materijali pokazuju učinke usklađivanja s efektivnim poljima usklađivanja Bφ razmjernim nφ. Polje Bφ čini prirodnu ljestvicu polja za zapinjanje vrtloga u takvim sustavima. Medutim, u poljima daleko od Bφ dolazi do miješanja različitih mehanizama zapinjanja vrtloga. Sažeto se razmatra utjecaj ovih saznanja na buduće pojačanje zapinjanja vrtloga u nanostrukturiranim Bi2223 i MgB2 supravodičima.

MgB2/Cu wires and tapes have been prepared using the powder-in-tube and reaction in-situ techniques.

Magnetoresistivity and critical current density were measured on five Si-nanoparticle doped (c=28 K in magnetic fields B>Bphi).

The magnetoresistivity and critical current density of five Si-nanoparticle doped ($c\leq 10$ wt\%) and undoped Cu-sheathed MgB$_{;2};$ tapes and wires have been measured for temperatures $T\geq 28$ K in magnetic fields $B\leq 0.95$ T. The irreversibility lines $B_{;irr}; (T)$ for doped tapes show a change in a slope of the temperature variation with a crossover field depending on Si-content. Such $B_{;irr}; (T)$ variation is typical for high-temperature superconductors (HTS) containing columnar defects (a crossover occurs around the matching field $B_{;\phi };$) and is very different from a smooth $B_{;irr}; (T)$ variation in undoped MgB$_{;2}; $ samples. However, in nanoparticle doped MgB$_{;2}; $, the enhancement of $B_{;irr}; $ with respect to that of the undoped one, persists at all field scales (including $% B\gg B_{;\phi }; $), which is not the case in HTS containing columnar defects. The microstructure studies of nanoparticle doped MgB$_{;2}; $ samples show uniformly dispersed Mg$_{;2}; $Si nanopercipitates, which probably act as a correlated disorder. The observed difference between the field variations of the critical current density and pinning force density of the doped and undoped samples support the above findings. The impact of these results for a further enhancement of flux pinning and critical currents in MgB$_{;2}; $ is briefly discussed.

Nedavno je opaženo da dodatak različitih nanočestica (npr. SiC, Si, C, Y$_{; ; ; 2}; ; ; $O$_{; ; ; 3}; ; ; $) jako pojačava zapinjanje magnetskih vrtloga u supravodiču MgB$_{; ; ; 2}; ; ; $. Mehanizam tog pojačanja za sada još nije razjašnjen. U cilju rješenja tog problema, sustavno smo mjerili magnetootpor i kritične struje dviju MgB$_{; ; ; 2}; ; ; $ traka obloženih bakrom, od koji je jedna bila dopirana s 5 tež.\% Si-nanočestica veličine 50 nm. Mjerenja izvršena u području temperatura $T\geq 28$ K i magnetskih polja $B\leq 1$ T su nam omogućila da precizno odredimo temperaturne ovisnosti ireverzibilnih polja $B_{; ; ; irr}; ; ; $ (za $B\leq B_{; ; ; irr}; ; ; $ je tok struje kroz supravodič nedisipativan) i poljne i temperaturne ovisnosti gustoća kritičnih struja $J_{; ; ; c}; ; ; $ i volumnih sila zapinjanja vorteksa $F_{; ; ; p}; ; ; =J_{; ; ; c}; ; ; B$ za oba uzorka. Monotono snižavanje $B_{; ; ; irr}; ; ; $ s porastom temperature opaženo u nedopiranom uzorku je u dopiranom zamijenjeno izrazitim koljenom na $T=35$ K što ukazuje na zapinjanje vorteksa na koreliranim jakim centrima zapinjanja. Sukladno strukturnim istraživanjima, ti centri zapinjanja su fino raspršene Mg$_{; ; ; 2}; ; ; $Si nanočestice ($\leq 10$ nm) nastale tijekom sinteze uzorka. Ponašanje kritičnih struja i volumnih sila zapinjanja također su u skladu s iznesenim zaključcima. Dok je skaliranje $F_{; ; ; P}; ; ; -B$ krivulja u nedopiranom MgB$_{; ; ; 2}; ; ; $ uzorku slično onom u Nb$_{; ; ; 3}; ; ; $Si (zapinjanje na granicama zrna), ono u dopiranom uzorku više je nalik ponašanju opaženom u visokotemperaturnim supravodičima s uvedenim stupčastim defektima (korelirani defekti).

Ranije smo pokazali da stupčasti defekti promjera $\sim 5$ nm nastali ozračivanjem termičkim neutronima Bi2223 vrpci dopiranim s $^{; ; ; 235}; ; ; $U\ (U/n procesiranjem) tvore jake individualne centre zapinjanja kvanata magnetskog toka $\Phi _{; ; ; 0}; ; ; $ koji jako povisuju ireverzibilna polja $B_{; ; ; irr}; ; ; $ (za $B\leq B_{; ; ; irr}; ; ; $ je tok struje kroz supravodič nedisipativan) i poboljšavaju poljnu ovisnost kritičnih struja $J_{; ; ; c}; ; ; (B)$ u tim materijalima na $T=77$ K te za $B\leq 1 $ T. Proširenjem tih istraživanja na široko područje temperatura $T\geq 30$ K i polja $B\leq 5$ T, pokazali smo da su pojačanje zapinjanja vrtloga (izraženo putem $B_{; ; ; irr}; ; ; (T)$ i potencijala zapinjanja $U_{; ; ; 0}; ; ; $) i s njim povezano poboljšanje $J_{; ; ; c}; ; ; (B)$ ovisnosti (izraženo poljem $B_{; ; ; \max }; ; ; $ na kojem je volumna sila zapinjanja $F_{; ; ; p}; ; ; =J_{; ; ; c}; ; ; B$ maksimalna) u tim materijalima univerzalne funkcije plošne gustoće stupčastih defekata $n_{; ; ; \phi }; ; ; $ (time i njoj pridruženog polja podudaranja $B_{; ; ; \phi }; ; ; =n_{; ; ; \phi }; ; ; \Phi _{; ; ; 0}; ; ; $). Konkretno, $B_{; ; ; \phi }; ; ; (n_{; ; ; \phi }; ; ; )$ čini univerzalnu poljnu ljestvicu pomoću koje se sva svojstva ovih sustava povezana sa zapinjanjem vrtloga mogu skalirati (u prikazu prema $B/B_{; ; ; \phi }; ; ; $ polazuju univerzalnu ovisnost). Time je iz poznatog $B_{; ; ; \phi }; ; ; $ moguće predvidjeti ponašanje danog sustava, odnosno moguće je unaprijed odabrati najpovoljniji sustav za danu uporabu. Stoga uz značajnu konceptualnu važnost (priroda zapinjanja vrtloga na nasumično usmjerenim stupčastim defektima), ova istraživanja imaju i prvorazrednu aplikativnu važnost (ukazuju na način proizvodnje supravodiča koji se može koristiti u magnetskom polju na odabranoj povišenoj temperaturi). Očekujeme da ovi rezultati dobiveni za U/n procesirane Bi2223 vrpce vrijede za bilo koji supravodič u kojemu vrtlozi zapinju na koreliranim defektima, neovisno o vrsti defekata.

Systematic analysis of the transport critical current densities Jc at 77 K for 235Uoxide (UO2 · 2H2O) doped Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes (Bi2223) irradiated with thermal neutrons is presented. Within the explored range of U-oxide concentrations (c ≤ 2 wt%) and neutron fluences (φ ≤ 6 · 1019 n/m2), the pinning of vortices in irradiated tapes increases approximately linearly with fission track density (proportional to cφ), as evidenced by progressively weaker magnetic field dependence of Jc on increasing cφ. Accordingly, the crossover field B∗ at which the pinning force density Fp reaches its maximum value Fp max = JcB∗ and the irreversibility field Birr(Fp → 0) increase approximately linearly with cφ. Therefore, Jc − B and Fp − B variations for all tapes with vortex pinning dominated by fission tracks show universal scaling behaviour with the scaling parameter B∗ (proportional to cφ). Taking into account the adverse effects of c and φ on Jc of our tapes, we estimate a maximum B∗ and Birr that can be reached in 235U-oxide doped Bi2223 tapes at 77 K., Predstavljamo sustavnu analizu transportnih gustoća kritične struje Jc na 77 K sa 235U-oksidom (UO2 · 2H2O) dopiranih, srebrom obloženih (Bi,Pb)2Sr2Ca2Cu3Ox vrpci ozračenih termičkim neutronima. U istraživanom području koncentracija U-oksida (c ≤ 2 tež.%) i toka neutrona (φ ≤ 6 · 1019 n/m2), zapinjanje magnetskih vrtloga u vrpcama raste približno linearno s gustoćom fisijskih tragova (razmjernoj sa cφ), što se ogleda u sve slabijoj ovisnosti Jc o magnetskom polju pri porastu cφ. U skladu s time, prijelazno polje B∗ na kojem gustoća sile zapinjanja Fp postiže najveću vrijednost Fp max = JcB∗ i ireverzibilno polje Birr(Fp → 0) rastu približno linearno s cφ. Zbog toga, Jc − B i Fp − B ovisnosti za sve vrpce u kojima je zapinjanje vrtloga pretežito zbog fisijskih tragova pokazuju univerzalno skaliranje s parametrom skaliranja B∗ (razmjerno cφ). Uzimajući u obzir negativni utjecaj c i φ na Jc naših vrpci, procijenili smo najveća polja B∗ i Birr koja se mogu postići u srebrom obloženim (Bi,Pb)2Sr2Ca2Cu3Ox vrpcama dopiranim s 235U-oksidom na 77 K.

Systematic analysis of the transport critical current densities Jc at 77 K for 235U-oxide (UO2*2H2O) doped Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Ox tapes (Bi2223) irradiated with thermal neutrons is presented.

m-H loops for virgin and neutron irradiated bulk and powder samples of MgB_{2} were measured in the temperature range 5-30 K in magnetic field B, 5 pages, 4 figures

Proučavan je utjecaj dopiranja 235U-oksidima i ozračivanja termičkim neutronima na električka transportna svojstva Bi-Sr-Ca-Cu-O srebrom oklopljenih vrpci.

Linija ireverzibilnosti u Bi2212 i Bi2223 supravodičima. Kvantno tuneliranje magnetizacije kod Mn12 acetata. Priroda procesa magnetiziranja vrpčastih mekih feromagnetika

The magnetoresistance of a (Bi,Pb)2Sr2Ca2Cu3O10+y Ag sheathed tape was measured in the temperature range 15 K ≤ T ≤ 120 K and magnetic field B ≤ 15 T applied perpendicular to the broader surface of tape. Throughout the explored field range, the onset of resistivity shows Arrhenius behaviour ρ ∝ exp(−U∗(1 − T /Tcs)/kBT B0.5) where U∗ is the sample dependent constant, and Tcs is the temperature somewhat higher than the temperature of the resistivity onset. The observed resistance variation can be attributed to a thermally activated flux flow in a highly viscous vortex-liquid regime characterized by a plastic deformation of vortices. Experimentally determined resistive irreversibility line Birr vs. Tirr follows the power-law dependence Birr(Tirr) ∝ (Tcs/Tirr − 1)2 which can be derived from the exponential behaviour of resistivity. Our Birr(Tirr) data can also be fitted by the combination of the Josephson coupling model and depinning of pancake vortices. This fit provides very reasonable values for Bc2, Bc1, Bc, ξab and λab of Bi2223 compound, and removes the unphysical divergence of Birr(T → 0) resulting from the above power-law fit., Mjerili smo magnetootpor (Bi,Pb)2Sr2Ca2Cu3O10+y vrpce obložene srebrom za temperature 15 K ≤ T ≤ 120 K i u magnetskim poljima B ≤ 15 T okomitim na širu plohu vrpce. U svim poljima početak otpora pokazuje Arrheniusovo ponašanje ρ ∝ exp(−U∗(1 − T /Tcs)/kBT B0.5), gdje je U∗ konstanta ovisna o uzorku, a Tcs je temperatura nešto viša od temperature pojave otpora. Primijetili smo da se ovisnost otpornosti može pripisati termički pobuđenom tečenju toka u jako viskoznom području tekućine magnetskih vrtloga karakteriziranom plastičnim deformacijama magnetskih vrtloga. Eksperimentalno određena otporna linija ireverzibilnosti Birr(Tirr) slijedi potencijsku ovisnost Birr(Tirr) ∝ (Tcs/Tirr − 1)2 koja se može izvesti iz eksponencijalnoe ovisnosti otpornosti. Naši Birr(Tirr) podaci isto tako mogu se prilagoditi modelu Josephsonovog vezanja i otpinjanja magnetskih vrtloga–palačinki. Ova prilagodba daje razumne vrijednosti parametara Bc2, Bc1, Bc, ξab i λab Bi2223 spoja, te uklanja nefizikalnu divergenciju Birr(T → 0) koja se dobiva iz potencijske ovisnosti.

A number of techniques by which effective pinning centres can be introduced to improve...

We have studied Jc-B-T surfaces for high-Jc Ag-clad Bi2Sr2CaCu2O8+x (Bi2212) and (Bi,Pb)2Sr2Ca2Cu3O10+y (Bi2223) tapes in the temperature range 4.5 - 100 K and magnetic field B Ł 1 T. In both types of tapes, for temperature T ł 0.5 Tc, Jc(T,B) and the pinning force density Fp = Jc B exhibit scaling behaviour analogous to that observed in high-Tc single crystals and epitaxial films. The parallel study of the pinning potentials U0 and of the irreversibility fields Birr (deduced from the resistive transitions in the applied field) for the same tapes, revealed that the activation barrier U = U0(1-T/Tc)/Bm determines both the magnitudes and temperature dependency of the scaling fields B* (defined by Fp = Fpmax) and Birr. Considerably larger U0 for Bi2223 tape, compared to that of Bi2212 tape, is probably due to both lower electronic anisotropy of this compound and higher content of defects. However, in both types of tapes, the pinning of vortices is insufficient for the high-B high-T applications., Proučavane su Jc q B q T plohe srebrom obloženih Bi2Sr2CaCu2O8rx (Bi2212) i (Bi, Pb)2Sr2Ca2Cu3O10rx (Bi2223) vrpci u području temperatura 4.5 – 100 K i magnetskog polja B s 1 T. Jc t T u Bv i gustoća sile zapinjanja Fp w JcB, u obje vrste vrpci, pokazuju normiranje slično onom u monokristalima i epitaksijalnim slojevima visokotemperaturnih supravodiča, za temperature T s 0 x 5 Tc. Paralelno istraživanje potencijala zapinjanja U0 i ireverzibilnih polja Birr (određenih iz otpornih prijelaza u magnetskom polju) pokazuju da aktivacijske barijere U w U0 t 1 q T y Tc v y B m određuju veličine i temperaturne ovisnosti normirajućih polja Bz (definiranih s Fp w Fpmax) i Birr . Znatno veći U0 za Bi2223 traku u usporedbi s onim Bi2212 trake, pripisuje se nizoj anizotropiji tog spoja i višem stupnju strukturnih nesavršenosti. Međutim, u obje vrste vrpci zapinjanje magnetskih vrtloga nije dovoljno za njihove primjene u jakim poljima i pri visokim temperaturama.

Critical current densities Jc and pinning energies U for two high-Jc Ag-clad Bi2Sr2Can− 1CunOx tapes with N=2 and 3 respectively have been studied in the temperature range 7– 110K and magnetic field B

We have studied J_c-B-T surfaces for high-J_c Ag-clad Bi_2Sr_2CaCu_2O_8+x (Bi2212) and (Bi,Pb)_2Sr_2Ca_2Cu_3O_10+y (Bi2223) tapes in the temperature range 4.5 - 100 K and magnetic field B < 1 T.

With high upper critical fields, high temperature superconductors (HTSC) have been recognised as candidate materials for coil and magnet applications. High field devices, at one time or another, when operated close to their rated limits are often faced with instability problems which normally are electrical, magnetic or mechanical in nature. The determination of stability parameters, therefore, is of interest to the conductor designer which very much assists in the processing aspect of long length production of wires and tapes. Due to the morphology of the superconductor most HTSC devices made with Bi(Pb)-2223 precursor exist in tape form. Here the determination of stability parameters (for flux-jump and cryogenic stability) for multifilamentary Bi(Pb)-2223/Ag tapes are presented. Processing parameters such as intermediate deformation and filling factors have been found to play a crucial role, not only on the critical current density of the tapes but on the stability aspect in conductor design as well.

Bi-2212/Ag tapes

The main results of the systematic study of the electron transport properties and AC susceptibility in Pb-doped, almost single phase, Bi 2223 ceramic samples and Ag-clad Bi 2223 tape, are presented. Whereas the results for the ceramic samples can only be used for the study of the percolation problem in the weak-link network, those for tape can yield some intrinsic parameters of Bi 2223 compound (the upper critical fields BC2, the coherence lengths, etc.). In addition, the results for the tape provide some technologically relevant parameters (the pinning potential U0, volume pinning force Fp and the flux-flow viscosity h) and an insight into the nature of dissipation and pinning in these materials. Some factors limiting the critical current density Jc in the present-day tapes are briefly discussed., Prikazani su glavni rezultati sustavnog istraživanja električnih svojstava i inicijalne susceptibilnosti gotovo–monofaznih Bi 2223 keramičkih uzoraka dopiranih olovom i srebrom obložene vrpce. Dok se rezultati za keramičke uzorke mogu primjenjivati isključivo za proučavanje perkolacije u sustavu slabih veza, oni za traku daju neke intrinsične parametre Bi 2223 spoja (viša kritična polja i duljine koherencije). Nadalje, rezultati za traku daju neke tehnološki važne parametre (potencijal zapinjanja U0, volumnu gustoću sile zapinjanja Fp i viskoznost tečenja magnetskih vrtloga η) i uvid u prirodu rasipanja energije i zapinjanja vrtloga u tim materijalima. Ukratko su razmotreni razlozi ograničenja kritičnih struja u vrpcama.

AC susceptibility and V-I characteristics of a well characterised Ag-clad Bi-Pb-Sr-Ca-Cu-O tape have been studied in the temperature (T) range 77-106 K and magnetic fields (B) up to 0.06 T. The intrinsic critical current density J_s (from ac susceptibility) is 30000 A/cm2 at 77 K whereas the transport critical current density Jc (from V-I curves) is 10100 A/cm2 at the same temperature. Both Js and Jc showed power law variations with T and B, respectively, characteristic for intragranular flux creep. From the dissipation within the core the differential resistance Rf (associated with the flux flow) has been deduced. The magnitude and the variations of Rf with T and B are consistent with those due to flux flow in type II superconductors in low field. From d^2 V/d I^2 vs I curves very broad critical current distribution CCD has been deduced.