Ar-annealed Sample Research Articles

Comparative study on slow-state near interface hole traps in NO and Ar annealed N-type 4H-SiC MOS capacitors by ultraviolet light

The characteristics of near interface charge trapping and releasing on n-type 4H-SiC MOS capacitors with NO and Ar passivation have been systematically investigated through time-dependent bias stress with ultraviolet light irradiation. Flat band voltage instability of the Ar annealed samples mainly results from electrons directly tunneling in and out of the near interface electron traps. However, hole trapping by the near interface hole traps (NIHTs) also need to be concerned for the NO annealed samples. It is found that part of the trapped holes cannot be easily released from the slow-state NIHTs, which may act as the positive fixed charge and induce the unrecoverable negative shift of threshold voltage. The results from XPS show that after the NO annealing, some of the intermediate oxidation states are converted to the strong Si≡N and Si–Ox–Ny bonds located in the transition layer, which may act as NIHTs and even suppress hydrofluoric acid etching. Thus, it is important to optimize nitrogen treatment in order to reduce the density of NIHTs induced in the 4H-SiC MOS devices.

Strong visible and near infrared photoluminescence from ZnO nanorods/nanowires grown on single layer graphene studied using sub-band gap excitation

Fabrication and optoelectronic applications of graphene based hybrid 2D-1D semiconductor nanostructures have gained tremendous research interest in recent times. Herein, we present a systematic study on the origin and evolution of strong broad band visible and near infrared (NIR) photoluminescence (PL) from vertical ZnO nanorods (NRs) and nanowires (NWs) grown on single layer graphene using both above band gap and sub-band gap optical excitations. High resolution field emission scanning electron microscopy and X-ray diffraction studies are carried out to reveal the morphology and crystalline quality of as-grown and annealed ZnO NRs/NWs on graphene. Room temperature PL studies reveal that besides the UV and visible PL bands, a new near-infrared (NIR) PL emission band appears in the range between 815 nm and 886 nm (1.40–1.52 eV). X-ray photoelectron spectroscopy studies revealed excess oxygen content and unreacted metallic Zn in the as-grown ZnO nanostructures, owing to the low temperature growth by a physical vapor deposition method. Post-growth annealing at 700 °C in the Ar gas ambient results in the enhanced intensity of both visible and NIR PL bands. On the other hand, subsequent high vacuum annealing at 700 °C results in a drastic reduction in the visible PL band and complete suppression of the NIR PL band. PL decay dynamics of green emission in Ar annealed samples show tri-exponential decay on the nanosecond timescale including a very slow decay component (time constant ∼604.5 ns). Based on these results, the NIR PL band comprising two peaks centered at ∼820 nm and ∼860 nm is tentatively assigned to neutral and negatively charged oxygen interstitial (Oi) defects in ZnO, detected experimentally for the first time. The evidence for oxygen induced trap states on the ZnO NW surface is further substantiated by the slow photocurrent response of graphene-ZnO NRs/NWs. These results are important for tunable light emission, photodetection, and other cutting edge applications of graphene-ZnO based 2D-1D hybrid nanostructures.

Effect of annealing temperature on the dielectric and magnetic response of (Co, Zn) co-doped SnO2 nanoparticles

The effect of annealing temperature on the dielectric and magnetic properties of (Co, Zn) co-doped SnO2 nanoparticles under air/oxygen (O2) and argon (Ar) atmospheres at 600 °C have been systematically investigated. A significant decrease is observed in dielectric constant and dielectric loss resulting from the incorporation of Co and Zn into the SnO2 lattice. Higher dielectric constant and loss was observed in the O2 annealed sample. Moreover, the electrical conductivity of the (Co, Zn) co-doped SnO2 samples increased in comparison with that of pure SnO2 sample due to the increase of available charge carriers after replacement of Sn ions with Co and Zn ions. Room-temperature ferromagnetism (RTFM) was observed for both the O2 and Ar annealed (Co, Zn) co-doped SnO2 samples. However, the remanent magnetization (Mr) varied drastically for different environmental annealing processes with Mr = 0.412 and 0.20 memu/g for the O2 and Ar-annealed samples, respectively. The results show that the enhanced dielectric and magnetic properties of (Co, Zn) co-doped SnO2 sample is strongly correlated with the increase in O2 vacancies. These findings not only demonstrate that (Co, Zn) co-doped SnO2 samples show tunable RTFM, but also suggests that RTFM can be influenced by introduction of O2 vacancies during O2 annealing.

Synthesis and characterization of Ar-annealed zinc oxide nanostructures

Nanostructured zinc oxide samples were synthesized through CVD and annealed in argon. The samples were investigated using SEM, TEM, XRD, and UV/VIS/FTIR photoacoustic spectroscopy. The SEM/TEM images show relatively spherical particles that form elongated, connected domains post-anneal. XRD measurements indicate a typical wurtzite structure and reveal an increase in average grain size from 16.3 nm to 21.2 nm in Ar-annealed samples over pristine samples. Visible photoacoustic spectra reveal the contribution of defect levels on the absorption edge of the fundamental gap of zinc oxide. The steepness parameter of the absorption edge, which is inversely proportional to the width of the absorption edge, decreased from 0.1582 (pristine) to 0.1539 (annealed for 90 minutes) revealing increased density of defect states upon annealing. The FTIR photoacoustic spectra show an intense peak at 412 cm-1 and a shoulder at 504 cm-1 corresponding to the two transverse optical stretching modes of ZnO. These results may indicate a self-assembly mechanism upon anneal under Ar atmosphere leading to early-stage nanorod growth.

Effect of NO annealing on charge traps in oxide insulator and transition layer for 4H-SiC metal–oxide–semiconductor devices**Project supported by the National Natural Science Foundation of China (Grant Nos. 61404098 and 61274079), the Doctoral Fund of Ministry of Education of China (Grant No. 20130203120017), the National Key Basic Research Program of China (Grant No. 2015CB759600), the National Grid Science & Technology

The effect of nitric oxide (NO) annealing on charge traps in the oxide insulator and transition layer in n-type 4H–SiC metal–oxide–semiconductor (MOS) devices has been investigated using the time-dependent bias stress (TDBS), capacitance–voltage (C–V), and secondary ion mass spectroscopy (SIMS). It is revealed that two main categories of charge traps, near interface oxide traps (Nniot) and oxide traps (Not), have different responses to the TDBS and C–V characteristics in NO-annealed and Ar-annealed samples. The Nniot are mainly responsible for the hysteresis occurring in the bidirectional C–V characteristics, which are very close to the semiconductor interface and can readily exchange charges with the inner semiconductor. However, Not is mainly responsible for the TDBS induced C–V shifts. Electrons tunneling into the Not are hardly released quickly when suffering TDBS, resulting in the problem of the threshold voltage stability. Compared with the Ar-annealed sample, Nniot can be significantly suppressed by the NO annealing, but there is little improvement of Not. SIMS results demonstrate that the Nniot are distributed within the transition layer, which correlated with the existence of the excess silicon. During the NO annealing process, the excess Si atoms incorporate into nitrogen in the transition layer, allowing better relaxation of the interface strain and effectively reducing the width of the transition layer and the density of Nniot.

Mechanical and Transport Properties of Argon Annealed Y1 − x Ca x :123 Superconductors

We report here the effects of argon heat treatment at 450 ∘C for 12 h on two similar sets of oxygenated Y1 − xCax:123 superconducting samples prepared by two different heat treatments and oxygen purity as reported by Sedky and Abu-Ziad (Physica C 470, 659; 12). The oxygenated samples are called ssqHp, sssHp, ssqLp, and sssLp, and the Ar annealed samples are called ssqHpAr, sssHpAr, ssqLpAr, and sssLpAr. It is found that the c parameter of annealed samples is gradually increased with Ca addition for all samples, while orthorhombic distortion (OD) is decreased. It is also noted that Ar heat treatment decreased the link between superconducting grains for all samples, and a linear decrease in microhardness (Vickers hardness number (VHN)) with Ca addition is obtained. But the rate of increase/decrease of the c parameter, OD, and VHN against Ca content is different in ssqHpAr and sssLpAr samples as compared to sssHpAr and ssqLpAr samples. Interestingly, the sssHpAr and ssqLpAr samples show a considerable loss of oxygen and small decrease in Tc. While the ssqHpAr and sssLpAr samples show much smaller loss of oxygen and a gradual increase in Tc up to 16 and 17 K, respectively. These results are discussed in terms of the mechanism of oxygen loss by Ca in addition to ssqHpAr and sssLpAr samples as compared to sssHpAr and ssqLpAr samples.

Effects of annealing ambient on the photoluminescence properties of Si-rich oxide/SiO2 multilayer films containing Si-nanocrystals

In this study, Si-nanocrystals (Si-NCs) have been prepared by annealing Si-rich oxide (SRO)/SiO2 multilayer films in Ar and N2, and the effects of annealing ambient on the photoluminescence (PL) properties are studied. XPS results show that the chemical compositions for the SRO and SiO2 layers are SiO1.1 and SiO2, respectively. FTIR results show that phase separation between Si and SiO2 occurs after annealing treatment, and Si-NCs are obtained which have been proved by the TEM images. Large and high density Si-NCs are obtained in the Ar-annealed film, and high structural disorder exists at the interface of Si-NCs. Compared with the film annealed in N2, a 2.4 times PL enhancement is obtained for the Ar-annealed sample, and the PL peak shifts toward low energy. Two lifetime distribution bands are obtained by fitting the time-resolved PL spectra, and the proportion of slow PL decay component increases from 69.7 to 84.0 %. The PL intensity for the Ar-annealed film is further enhanced by hydrogen passivation, and the slow PL decay component is increased to 87.5 %. Analyses show that both interface states recombination and quantum confinement effect (QCE) related optical transition in the Si-NCs exist in the optical emission process, and intense PL can be obtained only when the QCE become dominant PL mechanism.

Effects of hydrogen, oxygen, and argon annealing on the electrical properties of ZnO and ZnO devices studied by current-voltage, deep level transient spectroscopy, and Laplace DLTS

Effects of annealing ZnO in hydrogen, oxygen, and argon have been investigated using deep level transient spectroscopy (DLTS) and Laplace-DLTS (LDLTS) measurements. Current-voltage (IV) measurements indicate a decrease in zero–bias barrier height for all the annealed samples. Conventional DLTS measurements reveal the presence of three prominent peaks in the un-annealed and annealed samples. A new peak with an activation enthalpy of 0.60 eV has been observed in the H2 annealed samples, while an estimated energy level of 0.67 eV has been observed in Ar annealed samples. O2 annealing does not introduce new peaks but causes a decrease in the concentration of the E3 peak and an increase in concentration of the E1 peak. The concentrations of all the intrinsic defects have decreased after H2 and Ar annealing; with Ar annealing giving peaks with the lowest concentrations. The E2 peak anneals out after annealing ZnO in Ar and H2 at 300 °C. From the annealing behaviour of E3, we have attributed to transition metal ion related defects, while E4 has been explained as a defect, whose formation favours oxygen deficient conditions. Laplace DLTS has successfully been employed to resolve the closely spaced energy levels in the E4 peak, splitting it into three peaks with energy levels, 0.68 eV, 0.58 eV, and 0.50 eV below the minimum of the conduction band for the Ar annealed sample.

Influence of the oxygen content on thermoelectric properties of Ca 3− xBi xCo 4O 9+ δ system

Oxygen contents and thermoelectric properties of hot-pressed polycrystalline Ca 3− x Bi x Co 4O 9+ δ (0.00 < x < 0.20) samples were investigated both in Ar and air atmospheres in the temperature range 300 K < T < 870 K. Ar-annealed samples showed reduction in electrical conductivity and an elevation in Seebeck coefficient at T > 650 K with increasing x, whereas no systematic behaviour was found for the air-annealed samples. The figure-of-merit ZT at 870 K was improved from 0.12 ( x = 0.00, both air and Ar) to 0.19 ( x = 0.20, air) and 0.15 ( x = 0.20, Ar). The results mark the significance of the oxygen content when assessing the thermoelectric properties of oxide compounds.

Nitrogen at theSi-nanocrystal/SiO2interface and its influence on luminescence and interface defects

The influence of the high-temperature annealing ambient, i.e., ${\text{N}}_{2}$ and Ar on size controlled Si nanocrystals (NCs) ranging from $\ensuremath{\sim}2$ to $\ensuremath{\sim}6\text{ }\text{nm}$ embedded in ${\text{SiO}}_{2}$ has been investigated in detail. Generally, ${\text{N}}_{2}$ annealing is proven to be beneficial as the dangling bond density (${\text{P}}_{\text{b}}$ defects at the $\text{NC}/{\text{SiO}}_{2}$ interface) is about half, accompanied by a doubled photoluminescence (PL) intensity. The PL blueshift of ${\text{N}}_{2}$ annealed samples compared to Ar-annealed samples (N-blueshift) was found to be pronounced only for small NCs whereas it appears to be insignificant for larger NCs. The origin of this N-blueshift was previously attributed to a growth suppression of the NCs by the presence of N during the annealing process. However, no evidence for this assumption is found by time-resolved PL, as the luminescence decay times are similar despite considerable N-blueshift. The exact location of the N incorporated during annealing was investigated by time-of-flight-SIMS and electron-spin resonance. Besides the distinct N enrichment in the NC layer, the ${\text{K}}^{0}$ center $(^{\ifmmode\bullet\else\textbullet\fi{}}\text{S}\text{i}\ensuremath{\equiv}{\text{N}}_{3})$ was detected indicating the formation of an interfacial N layer at the $\text{NC}/{\text{SiO}}_{2}$ interface. Elastic recoil detection analysis enabled the quantification of the incorporated N as well as the excess Si. Combined with transmission electron microscopy analysis (determination of NC size) the calculation of the NC density per superlattice layer and the thickness of the interfacial N layer were achieved. It turns out that $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{N}\text{ }\text{atoms}\text{ }{\text{cm}}^{\ensuremath{-}2}$ exist at the NC surface, which is well in accordance to the optimum value of the bulk $\text{Si}/{\text{SiO}}_{2}$ interface. These results strongly support our recently suggested explanation for the N-blueshift that is based on an increased NC band gap by the influence of interfacial N on the polarity of the surface terminating groups.

Magnetic properties and macroscopic heterogeneity of FeCoNbB Hitperms

Nanocrystalline ribbons of Fe 81− x Co x Nb 7B 12 (where x ranges from 0 to 40.5 at%) Hitperm alloys have been investigated as to their basic magnetic properties and the influence of the macroscopic heterogeneity. Different crystalline share at surfaces compared with the volume average is observed by conversion electron Mössbauer spectroscopy (CEMS) and Mössbauer spectroscopy (MS), respectively. This marks the presence of macroscopic heterogeneity in these Hitperms. The heterogeneity is generally more significant in Ar-annealed samples than in the vacuum-annealed ones. The characteristic slant hysteresis loops (hard-ribbon-axis) are seen as a rule with few exceptions. An inspection of hysteresis loop response of resin potted samples shows that the surfaces bi-axially squeeze the ribbon interior in heterogeneous Hitperms when the ribbons cool down after annealing. Certain compositions show macroscopic viscous flow prior to crystallization so the heterogeneity gets another chance to induce anisotropy during annealing. The induction attains 1.5 T but saturates poorly due to the heterogeneity and the ensuing anisotropy. Moreover the heterogeneity appears to hamper the crystallization within the ribbon interior. Unlike Finemets, the density of these Hitperms show no pronounced trend with annealing.

The Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/4H-SiC Interface Investigated by Thermal Dielectric Relaxation Current Technique

Al2O3 has been grown by Atomic Layer Chemical Vapour Deposition (ALCVD) on ntype 4H-SiC using O3 as an oxidant and tri-methyl-aluminum (TMA) as a precursor. After deposition, annealing at 1000°C during 3h in different atmospheres (Ar, N2 and O2) was performed. Interface properties were studied by Capacitance-Voltage (CV) and Thermal Dielectric Relaxation Current (TDRC) measurements. The highest near-interface trap density (Nit) was deduced to be 4x1012 eV-1cm-2 between 0.36 eV and 0.5 eV below the conduction band, Ec, for O2 annealed samples, 2.8x1012 eV-1cm-2 between 0.42 eV and 0.56 eV below Ec for Ar annealed samples and 2.2x1012 eV-1cm-2 between 0.4 eV and 0.6 eV below Ec for N2 annealed samples. Only samples annealed in Ar exhibit a nearly trap free region close to Ec. Annealing in N2 is found to decrease Nit between 0.3 and 0.7 eV but shows a slightly higher Nit close the conduction band compared to the Ar case.

Effect of annealing on dielectric behavior and electrical conduction of W6+ doped Bi3TiNbO9 ceramics

Bi 3 Ti 1 − x W x Nb O 9 + δ (x=0.15) (WBTN-15) ceramics were prepared using the solid state reaction method, and the behaviors of oxygen vacancies were confirmed and investigated by annealing the ceramic samples in O2 and Ar gas atmospheres. Dielectric measurements showed that oxygen vacancies had great contributions to the dielectric loss and constant of Ar-annealed sample, compared with those of as-sintered and O2-annealed samples. dc conductivity measurements indicate that oxygen vacancies played an important role mainly at lower temperature. The WBTN-15 ceramics exhibit intrinsic conduction mechanism at high temperature range and electronic and oxygen-vacancy ionic mixed conduction mechanism at low temperature range.

Neutron-diffraction study of structural transition and magnetic order in orthorhombic and rhombohedralLa7/8Sr1/8Mn1−γO3+δ

We report on a systematic neutron powder diffraction (NPD) study of polycrystallineLa7/8Sr1/8Mn1−γO3+δ compounds. We investigated the structural and magnetic phases and transitions in the temperaturerange between 10 and 900 K for two different samples: an Ar-annealed sample with an orthorhombicPbnm (Z = 4;O) structure at room temperature and an air-sintered sample with a rhombohedral (Z = 2;R) structure at room temperature. At higher temperatures, above 400 K, both samplesexhibit a rhombohedral structure. For the Ar-annealed sample, a Jahn–Teller (JT)transition occurs in the orthorhombic phase at about 298 K with very large variations in theMn–O2′ and Mn–O2 bond lengths and Mn–O1–Mn bond angle on cooling from 298 to 180 K.For this sample the ferromagnetic moment at 10 K in the magnetic space groupPb′n′m amountsto 3.22(5) μB/Mn.In contrast, the air-sintered sample undergoes on cooling a structural transition from rhombohedral(R) to orthorhombic (O) with a mixed phase of nearly equal R and O repartition at 120 K.Ferromagnetic order develops in this sample at about 240 K with a low-temperature moment of3.35(4) μB/Mn at 10 K. The coherent JT distortion in its orthorhombic phase occurs below some170 K. In addition, we have determined the coherent JT distortion parameterΔ, the tolerance factort and the one-electronbandwidth W of the eg-band.

Effect of low temperature annealing on doping level and superconducting properties for IBAD/PLD–YBCO coated conductor

The effect of low temperature annealing on the superconducting properties of PLD–YBCO tape has been investigated with varying atmosphere. The Tc of the as-prepared sample is 88.5K, for the sample post-annealed at 200°C in Ar atmosphere showed 91.5K, indicating Tc is sensitive to low temperature annealing. In spite of the higher Tc the Jc and μ0Hirr for the Ar-annealed sample were lower than those for the as-prepared sample. This indicates that the as-prepared PLD-YBCO tape is in the carrier overdoped state. It was found that re-annealing in which the sample was slowly cooled from 450°C in pure oxygen atmosphere could restore the Jc-degradation, demonstrating that oxygen absorption-release occurred reversely.

Retardation of strain relaxation in Si/SiGe/Si heterostructures during high temperature oxidation

The variations of strain stored in Si/Si 1− x Ge x /Si heteroepitaxial system with SiGe thickness below its critical thickness during high temperature oxidation (in O 2–C 2H 2Cl 2 ambient) or annealing (in Ar ambient) processing were investigated by ion channeling angular scan and high resolution X-ray diffraction. The retardation of strain relaxation in an oxidized sample compared with that in an Ar-annealed sample was observed. The depth profiles of Ge determined by SIMS indicated that Ge diffusion in the annealed sample is larger than that in the oxidized sample. The reduced diffusion of Ge in the oxidized sample compared to the Ar-annealed sample is responsible for retardation of strain relaxation.

Anomalous post-annealing effects on magnetic and electrical properties of La 0.8Ca 0.2MnO 3

We report anomalous post-annealing effects of La 0.8Ca 0.2MnO 3 under O 2 and Ar atmospheres. We have found that the critical temperature ( T C) of the as-prepared sample increases after Ar-annealing and decreases upon O 2 annealing. The temperature-dependent magnetization data of the as-prepared compound agree well with the sum of those of the O 2- and Ar-annealed samples. Colossal magnetoresistance (CMR) below 60 K that reaches to almost 100% is observed in the O 2-annealed sample. These unusual results are discussed in terms of global homogenization over the sample and magnetic inhomogeneity induced by the Mn deficiency.

Investigation of nitric oxide and Ar annealed SiO2/SiC interfaces by x-ray photoelectron spectroscopy

Silicon dioxide (SiO2)/silicon carbide (SiC) structures annealed in nitric oxide (NO) and argon gas ambiences were investigated using x-ray photoelectron spectroscopy (XPS). The XPS depth profile analysis shows a nitrogen pileup of 1.6 at. % close to the NO annealed SiO2/SiC interface. The results of Si 2p, C 1s, O 1s, and N 1s core-level spectra are presented in detail to demonstrate significant differences between NO and Ar annealed samples. A SiO2/SiC interface with complex intermediate oxide/carbon states is found in the case of the Ar annealed sample, while the NO annealed SiO2/SiC interface is free of these compounds. The Si 2p spectrum of the Ar annealed sample is much broader than that of the NO annealed sample and can be fitted with three peaks compared with the two peaks in the NO annealed sample, indicating a more complex interface in the Ar annealed sample. Also the O 1s spectrum of the NO annealed samples is narrow and symmetrical and can be fitted with only one peak whereas that of the Ar annealed sample is broad and asymmetrical and is fitted with two peaks. It is evident that the Ar annealed sample contains some structural defects at the interface, which have been removed from the interface by NO annealing as shown by O 1s spectra. The C 1s spectra at the interface reveal the subtle difference between NO and Ar annealed samples. An additional peak representing the interface oxide/carbon species is observed in the Ar annealed sample. At the interface, the N 1s spectrum is symmetrical and can be fitted with one peak, representing the strong Si≡N bond. However, the N 1s and C 1s XPS spectra acquired in the bulk of the dielectric showed not only the Si≡N bond but also a trace amount of the N–C bond.

Establishment of strongly overdoped states in theHgBa2Ca2Cu3O8+δsuperconductor

Strongly overdoped ${\mathrm{HgBa}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ (Hg-1223) samples with superconducting transitions as low as 97 K were successfully obtained by using HgO, ${\mathrm{Ca}}_{2}{\mathrm{CuO}}_{3},$ CuO, and mixtures of highly oxidized ${\mathrm{BaCuO}}_{2+\mathrm{\ensuremath{\epsilon}}}$ $(\ensuremath{\epsilon}\ensuremath{\approx}0.13)$ and/or ${\mathrm{BaO}}_{2}$ powders as starting materials for the high-pressure synthesis at 5 GPa and 950 \ifmmode^\circ\else\textdegree\fi{}C. The overdoped state was confirmed by observing negative values for the Seebeck coefficient throughout the temperature range from ${T}_{c}$ to 320 K in a thermoelectric power measurement. Also, both of the cell parameters $a$ and $c$ were found to decrease with decreasing ${T}_{c},$ reflecting, respectively, an increase in hole concentration in the ${\mathrm{CuO}}_{2}$ planes and the incorporation of oxygen into the ${\mathrm{HgO}}_{\mathrm{\ensuremath{\delta}}}$ layer. The oxygen excess \ensuremath{\delta} as determined by the $\mathrm{Cu}(+\mathrm{I})/\mathrm{C}\mathrm{u}(+\mathrm{I}\mathrm{I})$ coulometric titration method, was $\ensuremath{\sim}0.19$ in the overdoped sample with ${T}_{c}=107\mathrm{K}.$ Subsequent reducing annealing in an Ar atmosphere at 280 \ifmmode^\circ\else\textdegree\fi{}C increased the ${T}_{c}$ to 131 K. Consistently, only positive Seebeck coefficient values were observed up to 320 K for the Ar-annealed sample. A clearly underdoped material with ${T}_{c}=118\mathrm{K}$ was obtained by annealing the same sample in Ar at a higher temperature $(\ensuremath{\sim}400\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}).$ Finally, high-pressure synthesis starting from less-oxidized ${\mathrm{BaCuO}}_{2+\mathrm{\ensuremath{\epsilon}}}$ $(\ensuremath{\epsilon}\ensuremath{\approx}0.06)$ yielded a Hg-1223 material with $\ensuremath{\delta}\ensuremath{\approx}0.10$ and ${T}_{c}=132\mathrm{K}.$

Correlation between Cu valence, hole density and Tc of Bi2201, Bi2212 and Bi2223 superconductors

Abstract For the Bi2201 phase, by comparing the correlation between them with the Mott–Hubbard split model, it was found that while the correlation deviates from the Mott–Hubbard model for air-sintered samples, the correlation agree well with the Mott–Hubbard model for Ar-annealed samples. The deviation is believed to come from the destruction of the Mott–Hubbard character. For the air-annealed samples of Bi2212 phase, hole concentration, p scales very well with v, and the p–v line passes through the origin of the coordinates. However, the proportional constant is about two. The simplest explanation of the double proportional constant is to assume the coexistence of a hole of CuO2 character and BiO character. For the Bi2223 phase, only an Ar-annealed sample lied on the p=v line, suggesting that it has a Mott–Hubbard like electronic structure. However, the air-sintered and oxygen-annealed samples deviated unexpectedly far from the p=vline, indicating charge balance in the sample is drastically changed in the system. We made an accurate Tc vs v and Tc vs p diagrams for the Bi-based superconductors. While the Tc vs v diagram for the Bi2201 and 2212 superconductors showed a bell-shape, the Tc vs p diagram for those superconductors had a wide plateau on the top. The puzzling shape of Tc vs p diagrams is also explained by the two hole model. Around the plateau, mainly the number of hole of the BiO character is changed.