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It is a challenge to achieve flexibility in purely inorganic piezoelectric materials without organic support, and various thin film flexible inorganic piezoelectric materials has been developed recently. In this work, lead zirconate titanate (PZT) nanofiber membranes were prepared by electrospinning, and a flexible membranes can be obtained by reducing the calcination temperature, and the flexibility was characterized by the three-point method. The fiber membrane was relatively thicker in relative to thin films and confirmed to adsorb Congo Red quickly under the action of ultrasound. The maximum adsorption capacity is 61.78 mg g−1 and saturation time reaches 20 min under ultrasound treatment. In addition, the color change after saturation adsorption can quickly determine the actual load of the fiber membrane. In the future, this load saturation effect can be used to calibrate the relationship between the piezoelectric signal and the adsorption load, so as to obtain more accurate chemical sensors.

Traditional inorganic materials exhibit rigidity owing to the lack of polymer chains in polymer materials or atom slipping in metals. However, nanometerization has been recently proposed for the conversion of inorganic oxide materials into flexible materials. Herein, the flexible inorganic luminescent material, CaTiO3:0.2%Pr3+, was synthesized through electrospinning, and the macroscopic flexibility of pure inorganic CaTiO3:0.2%Pr3+ was achieved. The flexible membrane was characterized via X-ray diffraction, thermogravimetry, scanning electron microscopy (SEM), and photoluminescence analyses. The grain size was analyzed at various calcination temperatures via SEM, and the results suggested that the increase in the calcination temperature resulted in the growth of crystal grains. Studies have reported that the growth of crystal grains is beneficial for improving the luminescence performance; however, to obtain better flexibility, smaller crystal grains are required. This study provides an important reference for the design of flexible inorganic materials.

Piezoelectric catalysis is an emerging research field in recent years. Since the catalytic reaction usually occurs on the surface, the specific surface area is very important for piezoelectric catalysis. Therefore, nanoparticles and nanowires have been developed for piezoelectric catalysis and have attracted widespread attention. However, in actual water applications, the use of nanoparticles will cause secondary pollution. Therefore, an overall deformable nanoporous system is urgently needed to adapt to the shapes of various ultrasonic transducer heads. We have obtained macroscopically inorganic flexible barium titanate nanofiber membranes through electrospinning technology. Without traditional organic mixtures, the surface of the piezoelectric material can fully come into contact with water. The fiber membrane is macroscopically integrated, deformable, and can fully adapt to multiple ultrasonic transducers of various shapes. Calcium doping can effectively improve the catalytic effect, and the catalytic rate (k × 103) of the material with the highest doping concentration can reach 24.47 min−1. In addition, studies have found that lowering the calcination temperature can effectively improve the flexibility of the fiber membrane, which can be attributed to smaller barium titanate grains formed at low temperature. This work provides a generic method for preparing flexible inorganic piezoelectric materials that can be adapted to a variety of surfaces, and successfully applies it in the field of piezoelectric catalysis, which provides an important way for the practical research of piezoelectric catalysis in the future.

${\mathrm{Co}}_{2}$-based Heusler alloys show diverse magnetic behavior, extending from the localized Heisenberg to the delocalized itinerant, and thus cannot be generalized with one specific model. Therefore, we bring together experiments and first-principles calculations to reveal the origin of long-range ferromagnetism in the ${\mathrm{Co}}_{2}$-based Heusler alloy ${\mathrm{Co}}_{2}\mathrm{HfSn}$. The precise value of the critical exponents $\ensuremath{\beta}=0.471(4), \ensuremath{\gamma}=1.02(4)$, and $\ensuremath{\delta}=3.273(5)$ with the Curie temperature ($T{}_{c}=430$ K) were determined experimentally by means of different analytical methods such as modified Arrott plot analysis, the Kouvel-Fisher method, and critical isotherm analysis. The deduced critical exponents belong to the theoretical prediction of the three-dimensional mean-field model. The magnetic exchange distance is found to decay as $J(r)\ensuremath{\sim}{r}^{\ensuremath{-}4.52}$, indicating the long-range magnetic interaction in ${\mathrm{Co}}_{2}\mathrm{HfSn}$. Moreover, the magnetic entropy change $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}$ features a maximum at ${T}_{c}$, i.e., $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}^{max}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 29.87(6) J ${\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{4pt}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 5 T, whereas power law fitting of $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}^{max}$ with $H$ gives ${n}^{\ensuremath{'}}=0.663(5)$, also confirming the mean-field-type magnetic interaction in ${\mathrm{Co}}_{2}\mathrm{HfSn}$. Meanwhile, in order to explore the origin of long-range ferromagnetic ordering in ${\mathrm{Co}}_{2}\mathrm{HfSn}$, spin-polarized density functional theory calculations were employed in this study. No stable antiferromagnetic solution with stable local magnetic moments at the Co or Hf site was observed in our fixed spin moment simulation, revealing that ${\mathrm{Co}}_{2}\mathrm{HfSn}$ is a highly itinerant magnet with a long-range ferromagnetic solution together with robust half-metallic conduction stable against thermal excitation higher than room temperature. Furthermore, our theoretical analysis shows that ${\mathrm{Co}}_{2}\mathrm{HfSn}$ belongs to an unconventional family of itinerant magnetism. Both the 100% spin-polarized metallicity and ferromagnetism arise from the Co $d$ orbitals, causing it to be unique compared to the conventional itinerant family of Ni, Co, or Fe, where magnetism and metallicity originate from different orbitals characters.

Mn concentration of 6H-Ba3Ti2MnO9 was adjusted slightly to deviate from stoichiometric ratios. Our structural analysis shows that the spin dimer may form with Mn concentration slightly higher than stoichiometric. The magnetic properties are explored by combining DC magnetization and X-band (9.4 GHz) electron spin resonance (ESR). DC magnetization shows the signature of combination of frustrated spin and short-range spin. ESR shows that spin dimer can be formed in BaTi0.65Mn0.35O3, while no signature of spin dimer can be found in BaTi0.69Mn0.31O3 and Ba3Ti2MnO9.

The effects of Er 3+ ion doping on the lattice structure, magnetism, and ferroelectric properties of SmFeO 3 were investigated by X-ray diffraction (XRD), magnetic characterization, and ferroelectricity characterization. The results show that the lattice constant was reduced and the distortion became more significant after doping. Both the magnetic susceptibility and saturation magnetization were significantly enhanced, and the system was transformed from hard magnetic system to soft magnetic system. The electric polarization was also decreased with the doping.

3 He heat capacity of SmFeO 3 single crystal was carried out from 0.4 K to 10 K. Magnetization was also checked from 2 K to 300 K. Magnetization fitting obtains a reasonable Θ = −2.16 K, while no signature of magnetic phase transition can be found down to 0.4 K from specific heat, showing |Θ/T c | > 5.33. Considering the exchange interactions between Sm 3+ and Fe 3+ , Sm 3+ spins are frustrated. This gives a new form of spin frustration.

Layered perovskite-related Sm 6 Ti 4 Fe 2 O 20 compound was successfully synthesized through the intercalation of bilayer SmFeO 3 into the Sm 2 Ti 2 O 7 with pyrochlore structure by means of floating-zone melting technique. The microstructural properties were characterized using aberration-corrected scanning transmission electron microscopy and X-ray diffraction. Electron energy-loss spectroscopy investigation reveals that the Fe 3+ ions prefer to occupy the inner sites within the perovskite-like layers. This compound exhibits clearly the spin glass-like behavior as demonstrated by the magnetic properties measurement. Such complex magnetic behavior could be attributed to the partial chemical order of Ti/Fe over the B sites and the interactions between magnetic ions including Sm 3+ and Fe 3+ . In addition, the multiferroic behavior with the coexistence of the ferroelectricity and ferromagnetism was well established by magnetic and piezoresponse measurements.

The magnetic and electrical properties of the layered perovskite-related oxide, La6(Ti0.67Fe0.33)6O20, are investigated. The material possesses the structure of six ABO3 layers with iron ions concentrated towards the center of the slabs. The valence state of La, Ti and Fe ions was determined using X-ray photoelectron spectroscopy. The “glassy” magnetic behavior of La6(Ti0.67Fe0.33)6O20 can be understood by the coexistence and competition between two different types of interaction, which originate from both the antiferromagnetic interactions between Fe3+–O–Fe3+ in the central layers of the slabs and ferromagnetic coupling that is induced by the oxygen vacancies from the titanium ion enrichment zone at the borders, owing to the nonrandom distribution of magnetic Fe3+ ions. The observed ferromagnetism can be ascribed to the ferromagnetic coupling and spin canting of the antiferromagnetic coupling via the Dzyaloshinskii–Moriya interaction. The frequency-dependent behavior of the dielectric loss peak in La6(Ti0.67Fe0.33)6O20 manifests itself as a thermally activated relaxation process. The P–E hysteresis loops and local piezoresponse loops confirm the ferroelectric behavior of La6(Ti0.67Fe0.33)6O20.

The magnetic and electrical properties of hexagonal Ba3Ti2MnO9 are investigated. The material is a noncentrosymmetric evolution from hexagonal BaTiO3 with a space group P63mc. The existence and distribution of both Mn4+ and Ti4+ are checked using an electron energy-loss spectroscopy line scan by high resolution transmission electron microscopy. Magnetic transitions are attributed to the short range ordering and magnetic frustration. The frequency independent behavior of the dielectric peak shows a ferroelectric transition at 222 K. Both Positive Up and Negative Down (PUND) techniques and the local piezoresponse confirm the ferroelectric behavior of Ba3Ti2MnO9.

The layered perovskite-related oxide Nd6Ti4Fe2O20 was prepared by incorporating NdFeO3 in the host Nd2Ti2O7 using floating-zone melting technique. XRD and HRTEM results suggested that the material has a layered structure of n = 6 type. Nd6Ti4Fe2O20 exhibited spin glass-like behavior, and its magnetic behavior was affected by magnetic Nd3+ ions strongly at low temperature. The ferromagnetic and ferroelectric properties were observed by magnetic and PFM measurements at the room temperature. UV–Vis absorption spectroscopy revealed that the compound is a visible light absorbing photocatalyst with a direct band gap of 2.2 eV. In addition, the photocatalytic behaviors of bulk Nd6Ti4Fe2O20 were evaluated by photodegradation of rhodamine B under visible light irradiation.

Li 1− x Na x Cu 2 O 2 ( x =0, 0.05, 0.10, and 0.20) single crystals were synthesized by the self-flux method, and the temperature dependent magnetic susceptibility χ( T ) were measured along the c axis. Na doping at the Li sites induces almost no change in the temperature (about 40 K) corresponding to the maximum of magnetic susceptibility. However, it results in the upturn of the magnetic susceptibility in the low temperature region ( T T >60 K) of all the samples were well fitted by the spin S =1/2 chain frustrated model. The exchange coupling constants J 1 (ferromagnetic interaction) and J 2 (antiferromagnetic interaction) both decrease smoothly with the increase of the doping level x , which is possibly related to the increase of lattice parameters. At the same time, the frustration parameter α = J 2 / J 1 is unchanged, resulting in the unchanged temperatures corresponding to the maximum of magnetic susceptibility ( T Max =40 K) and to the maximum probability of the magnetic transition ( T h =24 K). It indicates t h at α is the decisive factor for the frustrated systems.

Using dc magnetic susceptibility, electron spin resonance (ESR) and dielectric spectroscopy techniques, we investigate the magnetic and dielectric properties of Sr 7 Mn 4 O 15 , which has a layered structure with pairs of face-sharing octahedra Mn 2 O 9 . Magnetic susceptibility reveals the Neel temperature T N ∼70.5 K, above which Sr 7 Mn 4 O 15 manifests intense short range order. ESR spectra indicate the existence of a transition at about 370 K, confirming the suggested spin pairing in the Mn 2 O 9 units. In the dielectric spectra, a sudden drop of permittivity is observed at T N , revealing the existence of strong spin–lattice coupling in Sr 7 Mn 4 O 15 .

Transport properties in the a-b plane of Nd0.75Sr1.25CoO4 thin film as fabricated via a pulsed laser deposition technique have been investigated by means of measurements of resistivity and thermopower, respectively, in the temperature ranges of 76-300 and 80-310 K. The thermopower of the specimen revealed a mechanism of spin-dependent scattering of the charge carriers where its conduction could be well interpreted by the small polaron hopping conduction in the nonadiabatic regime at high temperatures and the two-dimensional variable range hopping of small polarons at low temperatures. Possible mechanisms for the polaronic conduction were also discussed in the article where several physical parameters of the specimen were determined using a small polaron hopping model and a better understanding of the strongly correlated electron system was achieved.

The doping effect of amorphous carbon (C) containing magnetic impurity in MgB2 bulk has been studied. Structural characterization by means of X-ray diffraction and the superconducting transition temperature, Tc, measurement indicate that little C effectively enters the MgB2 structure. This should be due to the lower sintering temperature. The upper critical field, Hc2, and irreversibility field, Hirr, of samples show no systematic evolution with C doping. However, critical current density Jc(H) performance is greatly improved with C doping at 4, 15, and 28 K, respectively. Corresponding to this case, scanning electron microscope (SEM) image indicates that the grain size in samples becomes very small and grain boundary is developing roundness with the increasing of C content. This should be intimately related with the increase of magnetic impurity along with C doping. The result is discussed.

DC magnetization M ( T ) and electrical resistivity ρ ( T ) have been studied in the temperature range of 4–300 K for (Cr99V 1)95Fe5 and (Cr99V 1)75Fe25 alloys. A minimum is observed near T N in ρ ( T ) curve for (Cr99V 1)95Fe5, which indicates the spin-density wave (SDW) antiferromagnetic transition. The progressive opening up of the SDW antiferromagnetic energy gap can be well described by a temperature-dependent energy gap function as 2 Δ ∝ T N − T . A paramagnetic–ferromagnetic transition is confirmed near T C in M ( T ) curve for (Cr99V 1)75Fe25, but no anomaly is observed around T C in ρ ( T ) curve that would be covered up by magnetic cluster-dependent scattering. The analyses indicated the magnetic clusters start to form at relatively high temperature above the transition temperature. T N and the SDW antiferromagnetism are rapidly depressed for Fe-poor (Cr99V 1)95Fe5 while T C and the ferromagnetism are rapidly increased for Fe-rich (Cr99V 1)75Fe25 by the substitution of light doping V for Cr.

Molecular vibrations of the polycrystalline Nd2−xSrxCoO4 are systematically characterized by powdered x-ray diffraction, Raman scattering and infrared spectra at different dopings as well as at different temperatures. Structural refinements reveal that all the specimens crystallize in the K2NiF4 structure with space group I 4 / m m m as is also confirmed by the phonon bands of Raman scattering and infrared transmittance. The frequency shifts of the phonon bands are found to be very well consistent with the elongation and/or contraction of the bond lengths. Moreover, for Nd0.75Sr1.25CoO4, the phonon bands of the Raman active modes seem to retrace the evolutions of magnetic and structural temperature.

Systematic studies of structural, magnetic, electronic, and elastic properties have been performed for the electron-doped manganite Sr0.95Ce0.05MnO3. The results show that light doping with Ce in place of Sr in SrMnO3 could stabilize the perovskite-type structure. The electronic transport and magnetism measurements show that the sample exhibits a charge ordering (CO) state below T CO ∼ 230 K , accompanied by softening of Young’s modulus due to a strong electron–phonon coupling. Cluster-glass behavior and the magnetoresistance (MR) effect are observed at low temperatures, resulting from the induced double-exchange (DE) ferromagnetic (FM) clusters embedded in the CO antiferromagnetic (AFM) matrix. Above T CO , the high temperature range appears to be dominated by local FM fluctuations, which is further supported by internal friction measurements. Our results indicate the existence of intrinsic magnetic inhomogeneity in electron-doped Sr0.95Ce0.05MnO3.

The Ru-doped Ruddlesden–Popper (RP)-type compounds Sr3Fe2−xRuxO7 ( x = 0 , 0.3, 0.6, 1.0 and 1.4) were synthesized and checked by X-ray diffraction (XRD). The doping dependencies of unit cell parameters, resistivity ( ρ – T ) and magnetization ( M – T ) were studied. Further, hysteresis ( M – H ) measurements were done on the sample x = 1.0 . Resistance measurements indicate that all the samples are insulators and electric transport properties fit the two-dimensional variable range hopping (VRH) model very well. Magnetism measurements show that a spin-glass state exists in all the measured samples when the temperature is lower than about 25 K. The temperature dependencies of the inverse molar magnetic susceptibility indicate that weak ferromagnetism occurs at a much higher temperature than that of glassy transition.

MgB 2 /Fe wires and MgB 2 /Ta/Cu wires were prepared through the in situ powder-in-tube method by using Mg and B powders at ambient pressure. The phase compositions, microstructural features are investigated by X-ray diffraction and scanning electron microscope. The transport critical current properties are measured by the standard four-probe technique. It is found that no impurity phase is formed in MgB 2 /Fe wire. At the same time, there are almost no reaction between iron and magnesium according to the results of X-ray diffraction analyses. In addition, it is found that MgB 2 grains in Fe clad are fined by comparing the micrograph of Fe-clad wire and Ta-clad wire. The high transport critical current density ( J c ) of 6.0 × 10 4 A/cm 2 (5 K, 4 T) and 5.2 × 10 3 A/cm 2 (15 K, 6 T) are obtained in the MgB 2 /Fe wire.

We have successfully fabricated mono- and multifilamentary MgB 2 wires and tapes with different sheathed metals such as Cu, Ta, NbZr and Fe by the powder-in-tube method. The phase compositions, microstructure features and superconducting properties are investigated by X-ray diffractometer, optical microscopy, SEM, standard four-probe technique and SQUID magnetometer. The results indicate that there is no reaction between the sheathed metals used here except Cu. For the Cu/Ta/MgB 2 wire, the irreversibility field achieves 6.6 T at 5 K and J c is higher than 10 5 A/cm 2 at 5 K in self-field. By using NbZr as a buffer layer, 18-filamentary Cu/MgB 2 tapes show a transport high J c of 8×10 4 A/cm 2 (10 K self-field). Remarkably, we prepared the Fe/MgB 2 wire with high transport J c of 5.6×10 4 A/cm 2 (15 K, 3 T) and 5.1×10 4 A/cm 2 (25 K, 2 T). The reasons for the improvement of J c in high fields were briefly discussed.

We have measured J c ( B , T ) mainly at 4.2 and 77 K under perpendicular external fields and parallel ones. The results make it possible to elucidate the critical state model theoretically and experimentally. In the present work, an attempt has been made to elucidate the critical state model of high- T c superconductors theoretically according the measured J c ( B , T ) characteristics. Possible explanations of hysteretic J c versus H e characteristic were presented and discussed.

Long dense MgB 2 wires were successfully fabricated through the in situ powder-in-tube method by using steel sheath with low carbon content. Short samples of MgB 2 /Fe wires were sintered at 650–850 °C for 2–5 h in argon. Critical current density ( J c ) of the wires was measured in the temperature range of 4.2–30 K in the magnetic field up to 3 T by standard four probe method. High J c values of 1.3×10 5 A/cm 2 in self-field and 7.5×10 4 A/cm 2 in 1 T at 15 K were obtained for MgB 2 /Fe wires. The microstructure observation for MgB 2 wires shows that no reaction between Fe and MgB 2 was found and MgB 2 /Fe wires have better grain connectivity and higher density than MgB 2 bulk samples. The grain connectivity in wires is better than MgB 2 bulk samples. The results indicate that the J c can be further improved to meet the requirement for applications by optimizing the process conditions.

Experiment on X-ray photoelectron spectroscopy of samples of Bi 2 Sr 2− x La x CaCu 2 O y has been performed to investigate the distribution of La atoms on the cation sites and the change of valence of Bi and Cu atoms. The analysis indicates that La mostly takes the place of Sr at Sr sites. An increase in the average valence of Bi and a decrease in that of Cu have been observed. The resistivity and thermoelectric power (TEP) of the samples have also been measured. The two-band model is applied to analyse the results of TEP.

Polycrystalline samples of Bi 2 Sr 2− x La x CaCu 2 O y and pure Bi2212 with different oxygen content have been prepared and studied by Raman spectroscopy. No frequency change of O Bi A g mode is observed. The O Sr A g mode exhibits remarkable downward frequency shift. The analysis indicates that the content of excess oxygen inserted into the Bi 2 O 2 layer is the important factor causing frequency shift of the O Sr A g mode.

The temperature dependences of the in-plane resistivity ab(T ) and out-of-plane resistivity c(T ) in Bi-2212 crystals covering the region from the underdoped to the overdoped regime have been measured. In the underdoped regime, ab(T ) deviates from a linear temperature dependence below a characteristic temperature T *, well above Tc, whose value decreases with increasing hole concentration. For underdoped crystals, ab(T) shows a typical S-shaped temperature dependence and ab = 0*+exp(-/T ) is satisfactorily obeyed over a much wider temperature range from slightly above Tc up to T *. Near the optimal region, the T -linear dependence of ab(T ) is maintained over a wide temperature interval. In contrast, a power law ab~Tn (n = 1.5-1.8) is followed in the overdoped regime. As regards the out-of-plane resistivity, on the other hand, c(T ) for the underdoped Bi2Sr2CaCu2Oy crystals shows a semiconductive behaviour, which is well described by the formula c = (C1/T)exp(C2/T ) + C3T + C4. The difference between the temperature dependences of c(T ) in the overdoped Bi2Sr2CaCu2Oy and Bi1.85Pb0.15Sr2CaCu2O8 + crystals, with basically the same values of Tc and nearly the same power-law temperature dependences of ab(T ) (ab~T 1.4), reveals that the inter-plane disorder in the form of oxygen vacancies and substituted cations acting as an extra blocking layer plays an important role in out-of-plane transport.

Here, we report the synthesis and super- conductivity of the La-doped iron-based compound Sm0.95La0.05O0.85F0.15FeAs; the resistivity and magnetic measurement indicate that the onset transition temperature as high as 57.3 K. This compound has the same crystal structure as ZrCuSiAs type tetragonal layered structure. The higher Tc compares to SmO0.85F0.15FeAs was attributed to partly La-substitution.

The in-plane resistivity ${\ensuremath{\rho}}_{\mathrm{ab}}(T)$ and the out-of-plane ${\ensuremath{\rho}}_{c}(T)$ have been extensively measured for the pure single-crystal ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}\mathrm{}}\mathrm{}(\mathrm{Bi}2212)$ annealed at different oxygen pressure. The ${\ensuremath{\rho}}_{c}(T)$ and anisotropy $[{\ensuremath{\rho}}_{c}(T)/{\ensuremath{\rho}}_{\mathrm{ab}}(T)]$ decreases rapidly with increasing carrier concentration. It is found that the out-of-plane resistivity decreases linearly with temperature down to about 120 K for the overdoped sample; its resistivity anisotropy is a weak temperature dependence. In the $\mathrm{ab}$ plane, the anisotropy is very weak and nearly independent of temperature. The data of ${\ensuremath{\rho}}_{c}(T)$ and ${\ensuremath{\rho}}_{c}(T)/{\ensuremath{\rho}}_{\mathrm{ab}}(T)$ are well fitted by the bipolaron theory proposed by Alexandrov and Mott.

The polycrystalline samples of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{y}$ (Bi2212) with different oxygen content, ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Cu}}_{2}{\mathrm{O}}_{y}$ and ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{y},$ have been characterized by x-ray-diffraction and Raman-scattering measurements. It is found that the $c$-axis parameter decreases with increasing doping concentration (Pr or La) or oxygen content. The softening of the ${O(2)}_{\mathrm{Sr}}{A}_{g}$ mode corresponds to the decrease of the $c$-axis parameter. The effect of Pr substitution for Ca on this mode is smaller than that of La substitution for Sr. The shift of the ${O(1)}_{\mathrm{Cu}} {B}_{1g}$ mode is related to the ionic size of the doping element. The ${O(3)}_{\mathrm{Bi}}{A}_{g}$ mode does not exhibit remarkable frequency shift since the $\mathrm{Bi}\ensuremath{-}O(3)\ensuremath{-}\mathrm{Bi}$ force constant nearly remains unchanged upon doping. The effect of oxygen content on the ${O(2)}_{\mathrm{Sr}}{A}_{g}$ mode in the Bi2212 system is in contrast to that on the corresponding ${O(4)}_{\mathrm{Ba}}{A}_{g}$ mode in the Y123 system. Change in valence is the dominating effect causing the frequency shift of the ${O(2)}_{\mathrm{Sr}} {A}_{g}$ mode.

In (Bi,Pb)2Sr2Ca2Cu3Ox silver-sheathed (Bi2223/Ag) tapes, melted liquid phase plays an important role to form the Bi2223 phase. We have added a small amount of B2O3 into Bi2223/Ag tapes to assist in inducing melted phase because B2O3 has a melting point (460°C) much lower than the general sintering temperature of the tapes, and studied the influence of B2O3 doping on the microstructure and critical current density (Jc) of Bi2223/Ag tapes. The results show that B2O3 doping is really effective to result in the faster growth and better alignment of the Bi2223 grains in the superconducting core and improve the magnetic field dependence of the Jc value.

In this paper, the systematic study of nanostruc- tured high-temperature superconducting materials is reported for the first time. Nanocrystalline-grained Bi Sr Ca Cu O was prepared by crystallizing the corresponding amorphous plates. The grain-growth and size-control techniques were studied. The phases occurring were investigated by means of X-ray diffraction, and the morphologies of the grains were observed by electron microscopy. The superconduct- ing properties, measured by resistance-temperature ( R T) and alternating current susceptibility-temperature (ac T) methods, are discussed. Probable research values of these mesoscopic-structured HTSC materials are also proposed. PACS: 74.72.Hs; 81.35.+k; 81.40.-z Since the discovery of high-temperature superconductivity (HTSC), researchers have directed their attention to various polycrystalline and single crystalline samples with large grain sizes (> 3000 nm). The superconductivity of nanocrystalline HTSC material has not been investigated to our knowledge. If the grain size were quite small and located in the meso- scopic range, it is expected that the physical and=or mechan- ical properties of the HTSC materials would no longer be independent of the grain size. The purpose of our research was to prepare the Bi Sr Ca Cu O samples with various grain sizes and study their physical properties. This research will be helpful for both the application of the HTSC materials and the understanding of high-temperature superconductiv- ity. On the basis of our experience of growing the Bi-based 2212 superconducting whiskers from the glassy state (1) and the principle of preparing nanocrystalline alloys by means of crystallization from amorphous alloys (2), we prepared the Bi Sr Ca Cu O samples with various grain sizes. The systematic study of the superconductivities of nanos- tructured high-temperature superconducting materials is re- ported for the first time in this paper. In fact, there have been many reports on the preparation of Bi-based supercon- ductors from the glassy state (3-7); however, attention has

The effect of rare earth ion size on the charge transfer and Raman spectra of the rare-earth-substituted Pb-based 1212 compounds (Pb 0.65 Sr 0.35 )Sr 2 (R 0.5 Ca 0.5 )Cu 2 O y (R = Y, La, Ce, Pr, Nd, Yb, Lu) has been studied systematically. X-ray diffraction showed that all the rare-earth-substituted samples were single phase of the Pb-1212 except R = Ce. The compound with R = Ce did not form under the same synthesis conditions. Both the a and c parameters increased monotonically with the substitution of larger size rare earth. AC susceptibility measurement revealed that all the samples showed superconducting transitions between 43 and 68 K except the largest ion La-substituted sample. T c showed a tendency to decrease with rare earth radius. Raman spectra of these samples illustrated that only one peak at about 540 cm −1 appeared for all the rare-earth-substituted samples in the range of 100 to 800 cm −1 . This peak was attributed to the vibration of the apical-O(2) in this system. Its frequency showed a tendency to increase with rare earth ion. The relationship between lattice parameter, superconductivity, apical-O(2) vibrational characteristic and ionic radius were discussed in this paper. Based on several experimental facts, our present Pb-1212 samples are considered to lie in the underdoped region of the T c - n diagram.

Samples of Bi 2 Sr 2 Ca 1− x Pr x Cu 2 O y have been characterized by resistivity and thermoelectric power measurements. All metallic samples show superconductivity with a maximum T c = 90 K at x = 0.2. The sample of x = 0.6 shows a crossover from hopping conduction at low temperature above T c to metallic conduction at high temperature. For the metallic samples below x = 0.6, the results of thermoelectric power are well fitted by both of a phenomenological band spectrum model and the Nagaosa and Lee model.

A metallic conducting effect has been observed in a blue emitting porous silicon sample. In the sample, which was prepared using a hydrothermal etching process followed by oxidation treatment at for 30 s, it was observed that the resistance decreased linearly with decreasing temperature and became constant near 10 K. A possible mechanism for the observed effect is discussed in view of the silicon quantum dot superlattice structure observed in the sample.

Two kinds of methods have been used to synthesize Pb 0.5 Sr 2.5 Y 0.6 Ca 0.4 Cu 2 O 7-y samples. The synthesized sample using the first method shows superconductivity, while that using the second method exhibits a localized behavior at low temperature. Thermogravimetric analysis (TGA) and electrical transport measurements have been carried out on superconducting and nonsuperconducting samples grown under the two kinds of synthesis conditions anti the effect of oxygen content on the transport and superconducting propertics is discussed briefly.

Samples of are characterized by thermoelectric power and variable-temperature x-ray diffraction. For the superconducting sample , S is positive in the whole measuring temperature range and weakly dependent on temperature; for the Ca-doped samples, , S shows a negative and strong dependence on temperature at low temperature for large x. It is striking that Ca doping leads to a sharp peak at about 200 K for either the superconducting samples or the nonsuperconducting samples . The strength of the peak increases with increasing x. Low-temperature x-ray diffraction shows that the lattice parameters decrease with decreasing temperature and an anomaly is observed at the corresponding temperature.

The effect of annealing conditions on the superconductivity of the Pb-based 1 2 1 2 phase Pb0.65Sr2.35Y0.5Ca0.5Cu2O y system was studied. The weight change of the samples was measured by thermogravimetric analysis (TGA). The phases occurring in the samples were detected by X-ray diffraction (XRD) and their superconducting transitions were determined by alternating current (a.c.) susceptibility measurements. The results showed that the oxygen occupancy sites of the samples annealed under various conditions were different, and the oxygen content or oxygen occupancy site affected the phase formation of the sample. It has been found that there is an optimum value of oxygen content at which TC is the highest, and the highest TC can be obtained only within a very narrow range of oxygen content.

The Hall coefficient {ital R}{sub {ital H}}, resistivity, and magnetoresistance have been measured in both superconducting polycrystalline samples of Nd{sub 1.85{minus}{ital x}}Ca{sub {ital x}}Ce{sub 0.15}CuO{sub 4{minus}{delta}} and nonsuperconducting samples of Nd{sub 2{minus}{ital x}}Ca{sub {ital x}}CuO{sub 4+{delta}} ({ital x}{le}0.3). Addition of Ca does not destroy the superconductivity, but dramatically changes the {ital R}{sub {ital H}} and eventually causes a change in sign of {ital R}{sub {ital H}} from negative to positive. The hole state in the CuO{sub 2} plane arises from the lattice distortion induced by Ca doping, which leads to the O {ital p} band going through the Fermi level. The negative magnetoresistance is closely related to the localization of conducting carriers. {copyright} {ital 1996 The American Physical Society.}

The electronic transport properties in Bi2Sr2CuOy crystals have been investigated with the focus on the localized behaviours at low temperature. It is found that in the passage of transition from metallic to insulating states the samples first show two-dimensional weak localization behaviour, and cross over to the variable-range hopping conduction corresponding to the strong-localization regime. We analyse the experimental results and suggest that the metal-insulator transition is caused by the effects of both disorder in the lattice and electron correlations.

Polycrystalline samples of Y0.4Pr0.6Ba2Cu3O7- delta have been prepared and characterized by X-ray powder diffraction, differential thermal analysis and temperature dependence of resistivity and AC susceptibility. We observed that both superconductivity and metallic conductivity were revived at x>or=0.75, accompanied by an orthorhombic-to-tetragonal transition. The superconducting transition temperature could be further enhanced by increasing the Sr content, suggesting that there is an ion-size effect on Tc at the Ba site. The results were discussed in terms of the Pr-O covalent bonding effect.

Cu 2p core-level spectra have been obtained on as-grown and reduced ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{\mathit{y}}$. The intensity ratio of the Cu 2p satellite to main peaks (${\mathit{I}}_{\mathit{s}}$/${\mathit{I}}_{\mathit{m}}$) is lower compared with the case of p-type cuprates. This characteristic is discussed on the basis of the crystal-chemical parameters. The bond valence sums (BVS) of each ion are calculated. It is found that the effective oxidation state of Cu is, in contrast to the p-type cuprate superconductors, less than 2+. The relationship among the BVS, the Madelung site potential difference \ensuremath{\delta}${\mathit{V}}_{\mathit{M}}$ between the in-plane O and Cu, and the Cu-O charge-transfer gap \ensuremath{\Delta} is discussed. It is pointed out that the relatively lower ${\mathit{I}}_{\mathit{s}}$/${\mathit{I}}_{\mathit{m}}$ of Cu 2p XPS spectra reflects the lower valence state of Cu, or relatively smaller values of \ensuremath{\Delta} as well as \ensuremath{\delta}${\mathit{V}}_{\mathit{M}}$.

Samples of nominal composition (Pb 1- x Cd x )Sr 2 (Y 0.5 Ca 0.5 )Cu 2 O y (0⩽ x ⩽0.6) synthesized at 1000°C in oxygen were investigated. All the as-prepared samples became superconducting at around 25 K, except x =0 and 0.1. For the superconducting samples, the content of Cd has little effect on T c onset . However, the same annealing at 560°C for 1 h in air which induced superconductivity in the non-superconducting “as-prepared” sample of x =0.1 led to the depression of the superconductivity of the “superconducting as-prepared” samples of 0.2⩽ x ⩽0.6. The post-treatments in air and oxygen (1 and 5 atm) substantially increase the resistivities at 300 K of the samples.

We have measured the ab-plane resistivity on a number of Bi2Sr2CuOy crystals from 4.2 K to 300 K. The as-grown crystals usually exhibit a minimum in their normal-state resistivity. The low-temperature electronic transport can be described by a hopping con