Current voltage analysis and band diagram of Ti/TiO2 nanotubes Schottky junction

We report variable temperature resistivity measurements and mechanisms related to electrical conduction in 200 keV Ni²⁺ ion implanted ZnO thin films deposited by vapor phase transport. The dc electrical resistivity versus temperature curves show that all polycrystalline ZnO films are semiconducting in nature. In the room temperature range they exhibit band conduction and conduction due to thermionic emission of electrons from grain boundaries present in the polycrystalline films. In the low temperature range, nearest neighbor hopping (NNH) and variable range hopping (VRH) conduction are observed. The detailed conduction mechanism of these films and the effects of grain boundary (GB) barriers on the electrical conduction process are discussed. An attempt is made to correlate electrical conduction behavior and previously observed room temperature ferromagnetism of these films.     

Dielectric properties and EMI shielding efficiency of polyaniline and ethylene 1-octene based semi-conducting composites

The preparation of polyaniline (PAni) was carried out by the oxidative emulsion polymerization of aniline and the semi-conducting composites were prepared by mixing it with a polyolefinic thermoplastic elastomer ethylene 1-octene copolymer (EN). Different electrical properties and electromagnetic interference shielding efficiency (EMI SE) of these composites were measured. The results revealed that the incorporation of PAni in EN increases the conductivity, dielectric constant, dielectric loss and EMI SE. These composites exhibit pressure dependent dielectric properties and may act as pressure sensor. There are increase in AC conductivity and decrease in dielectric constant with the increase in applied pressure on composites. A model correlation between EMI SE and AC conductivity at same frequency for the composites having maximum 40% of PAni was obtained through extrapolation and linear regression analysis, which shows that EMI SE has linear relationship with AC conductivity. Because of their semi-conductive behavior these composites can find application as antistatic materials and electromagnetic interference (EMI) shielding material.     

Cu掺杂LaMn1－xCuxO3体系的磁转变和导电行为研究

系统研究了LaMn_1-xCu_xO₃(x=0.05，0.10，0.20，0.30，0.40)体系的磁转变和导电行为.结果表明，在LaMnO₃反铁磁母体中掺杂极少量的Cu(x=0.05)使该体系在157K左右出现强的铁磁转变，随着Cu掺杂浓度的增加，居里温度逐渐降低，而铁磁性则是先增强后减弱.与磁特性相对应，样品的电阻率随着Cu掺杂浓度的增加表现出先减小后增大的特征，并且在整个测量温区内始终呈现绝缘体型导电行为——从顺磁绝 关键词： 1-xCu_xO₃')" href="#">LaMn_1-xCu_xO₃ 导电行为 磁特性     

Variable range hopping conductivity in manganites

The nature of variable range hopping (VRH) conductivity which is observed in the insulating state of doped rare-earth manganites with perovskite structure is considered in the two component model of metallic-like droplets embedded in dielectric matrix. When the density of the metallic droplets is less than the percolation limit, the system falls into the insulating state with VRH conductivity defined by inter granular tunneling and electrostatic barriers. With temperature increasing the VRH regime is transforming into the hopping regime of small radius polarons.     

Dielectric relaxation in TGS crystals doped with orthophosphoric and phosphorous acids

Polarization switching and temperature dependences of the complex permittivity of triglycine sulfate crystals doped with orthophosphoric and phosphorous acids are studied in the frequency range 100 Hz-1 MHz at temperatures of 140–340 K. It is found that, for a comparatively low solubility of the dopants (not over 1 mol %), doping of the crystals gives rise to a noticeable change in the parameters of the dielectric hysteresis loop, as well as in the magnitude and character of the temperature dependence of dielectric losses, thus implying an increase in the ferroelectric phase of the doped crystals of the activation energies and relaxation times of domain walls as a result of their interaction with the dopants.     

Salty Water in KOH-Doped Hexagonal Ice: a Proton and Deuteron NMR Study

Water doped with 10^?2 mol of KOH was cooled to temperatures at which most of the solution freezes to form hexagonal ice. Using proton and deuteron spin–lattice relaxometry as well as static field gradient diffusometry, it was found that a liquid-like phase coexists with the crystal down to below 200 K. The ionic dopants are expelled from the crystalline phase and form a KOH-enriched aqueous solution probably in the form of inclusions within the ice crystal. Its self-diffusion coefficient is only slightly smaller than that of nominally pure water. Motional correlation times were determined on the basis of spin–lattice relaxation times and compared with previous electrical conductivity and calorimetry results.     

非金属与金属原子共掺杂石墨烯体系的气敏特性研究

采用基于密度泛函理论的第一性原理方法研究了非金属N原子和金属原子(M=Mo,Al,Co,Fe,Au和Pt)共掺杂石墨烯体系(M-GN4)的电子结构和表面活性.研究发现:单个金属原子掺杂的GN4体系表现出不同的稳定性,相比掺杂的Au原子,其它的金属原子都具有很高的稳定性( 6. 0 e V).掺杂的金属原子失去电荷显正电性将有助于调控气体分子的吸附特性. Mo-GN4和Al-GN4衬底对吸附的O_2表现出较高的灵敏性,单个CO和O_2分子在Co-GN4和Fe-GN4衬底的吸附能差别较小.此外,吸附不同的气体分子能够有效地调控M-GN4体系的电子结构和磁性变化.     

Thermoelectric properties of homogeneously and non-homogeneously doped CdTe15/16M1/16 (M=N,P, As,Sb) and Cd15/16TeM1/16 (M=Na,K, Rb,Cs)

The electrical transport properties of p-doped semiconductors CdTe_15/16M_1/16 (M=N, P, As, Sb) and Cd_15/16TeM_1/16 (M=Na, K, Rb, Cs) with two configurations are investigated through first-principles calculations combined with Boltzmann transport theory under the relaxation time approximation. It is found that N and Cs atoms in the homogeneous structure induce much sharper electron densities of states (DOSs) and flatter energy bands at the valence band edges than the rest of doped elements, resulting in much larger Seebeck coefficients. The calculations reveal that most of the Seebeck coefficients and electrical conductivities are impacted unfavorably by the conglomeration of impurity atoms considered. Though the power factors for homogeneous doping of N and Cs are comparatively smaller, the electronic figures of merit are much larger at 800–1000 K than the rest ones due to much smaller electronic thermal conductivities, therefore probably enhancing the thermoelectric figures of merit. The results show that doping the elements with electronegativities distinct from the host atoms can enhance the Seebeck coefficients and the thermoelectric performances of bulk semiconductors efficiently if the energy levels of doped atoms resonate with those of host atoms and the arrangement of doped atoms is modulated appropriately to avoid deteriorating the sharpness of the DOS (or transport distribution).     

Eu掺杂TbMnO3多晶材料的介电性质

采用固相反应法制备了Tb_0.8Eu_0.2MnO₃多晶材料.对样品的X射线衍射（XRD）分析表明Eu³⁺固溶于TbMnO₃中.测量了样品在低温(100 K ≤T≤ 300 K)和低频下(200 Hz≤f≤100 kHz)的复介电性质.在此温度区间内发现了两个介电弛豫峰.经分析认为低温峰（T≈170 K）起源于局域载流子漂移引起的偶极子极化效应,而高温峰（T≈290 K）则是由离子电导产生的边界和界面层的电容效应引起的.电阻率的测量显示在低温下（T≈230 K）存在明显的导电机制转变. 关键词： 多铁性材料 掺杂 介电性质     

Magnetic field effects on excited states,charge transport,and electrical polarization in organic semiconductors in spin and orbital regimes

Magnetic field can influence photoluminescence, electroluminescence, photocurrent, injection current, and dielectric constant in organic materials, organic–inorganic hybrids, and nanoparticles at room temperature by re-distributing spin populations, generating emerging phenomena including magneto-photoluminescence, magneto-electroluminescence, magneto-photocurrent, magneto-electrical current, and magneto-dielectrics. These so-called intrinsic magnetic field effects (MFEs) can be observed in linear and non-linear regimes under one-photon and two-photon excitations in both low- and high-orbital materials. On the other hand, spin injection can be realized to influence spin-dependent excited states and electrical conduction via organic/ferromagnetic hybrid interface, leading to extrinsic MFEs. In last decades, MFEs have been serving as a unique experimental tool to reveal spin-dependent processes in excited states, electrical transport, and polarization in light-emitting diodes, solar cells, memories, field-effect transistors, and lasing devices. Very recently, they provide critical understanding on the operating mechanisms in advanced organic optoelectronic materials such as thermally activated delayed fluorescence light-emitting materials, non-fullerene photovoltaic bulk-heterojunctions, and organic–inorganic hybrid perovskites. While MFEs were initially realized by operating spin states in organic semiconducting materials with delocalized π electrons under negligible orbital momentum, recent studies indicate that MFEs can also be achieved under strong orbital momentum and Rashba effect in light emission, photovoltaics, and dielectric polarization. The transition of MFEs from the spin regime to the orbital regime creates new opportunities to versatilely control light-emitting, photovoltaic, lasing, and dielectric properties by using long-range Coulomb and short-range spin–spin interactions between orbitals. This article reviews recent progress on MFEs with the focus on elucidating fundamental mechanisms to control optical, electrical, optoelectronic, and polarization behaviors via spin-dependent excited states, electrical transport, and dielectric polarization. In this article both representative experimental results and mainstream theoretical models are presented to understand MFEs in the spin and orbital regimes for organic materials, nanoparticles, and organic–inorganic hybrids under linear and non-linear excitation regimes with emphasis on underlying spin-dependent processes.     

Effect of substitutions on dielectric behavior of La2NiMnO6

The substituted La₂NiMnO₆ (LNMO) double perovskite powder samples are prepared by hydroxide co-precipitation method. The electrical properties such as conductivity, dielectric constant and impedance analysis of the substituted sample, have been studied. The activation energy is determined by dc conductivity plot gives the fair idea of conduction mechanism. The dielectric and impedance analysis suggests the contribution of extrinsic and intrinsic effects in dielectric relaxation due to substitution at A and B site cations. The Nyquist plot reveals the role of grain and grain boundaries in charge conduction mechanism. The large grain and grain boundary resistance value and activation energy ～100 meV of substituted LNMO samples shows the presence of variable range hopping (VRH) conduction mechanism.     

Slow Relaxation in Ice and Ice Clathrates and its Connection to the Low-Temperature Phase Transition Induced by Dopants

We have used dielectric spectroscopy (frequency range: 10 6 Hz-10 m 3 Hz) and differential scanning calorimetry down to a temperature of 77 K, to study the effect of various dopants on the molecular relaxation in hexagonal ice ( I h ) and some clathrate hydrates ( I c ). The nonelectrolytic dopants did not affect a large change in the dynamics. However, when I h and I c are doped with the alkali hydroxides: KOH, NaOH, LiOH and Ca(OH) 2 , a drastic fall in the relaxation times of the order of 10 7 -10 12 has been noticed. It appears that the alkali metal- and hydroxyl-ion pair exert a large influence on the orientational mobility of water molecules by way of polarization over a domain. The amount of phase that gets transformed to the low temperature (low- T ) ordered phase depends on the solid solubility of the dopant. The nature of the relaxation and variation of the static dielectric constant have been examined critically to get an insight into the actual mechanism responsible for the above phenomena. Our studies confirm the earlier views of Tajima et al . (1984) J. Phys. Chem. Solids , 45 , 1135, that the low- T phase transition which has so far escaped observation for kinetic reasons has now revealed itself by the catalytic action of the dopants.     

Effect of dopants on the structural,optical and electrical properties of sol–gel derived ZnO semiconductor thin films

Undoped, Ga-, In-, Zr-, and Sn-doped ZnO transparent semiconductor thin films were deposited on alkali-free glasses by sol–gel method. 2-methoxyethanol (2-ME) and diethanolamine (DEA) were chosen as a solvent and a stabilizer, respectively. The doping concentration was maintained at 2 at.% in the impurity doping precursor solutions. The effects of different dopants on the structural, optical, and electrical properties of ZnO thin films were investigated. XRD results show that all annealed ZnO-based thin films had a hexagonal (wurtzite) structure. ZnO thin films doped with impurity elements obviously improved the surface flatness and enhanced the optical transmittance. All impurity doped ZnO thin films showed high transparency in the visible range (>91%). The Ga- and In- doped ZnO thin films exhibited higher Hall mobility and lower resistivity than did the undoped ZnO thin film.     

Structural and electrical impedance study of Pb(Sr1/3Nb2/3)O3

Lead-based ceramic Pb(Sr_1/3Nb_2/3)O₃ (PSN) is prepared by the columbite precursor method and structurally characterized using XRD. The X-ray diffraction shows a perovskite structure with cubic pyrochlore phase. Detailed studies of ε′ and ε″ of the compounds show that the compounds exhibit dielectric anomaly. Impedance spectroscopy is used to characterize the electrical behaviour. Results indicate that the relaxation mechanism of the material is temperature dependent and has dominant bulk contribution in different temperature ranges. Modulus spectroscopic data were used to gain an insight into the electrical properties of the samples and with a view to observe the relaxations in them. Frequency dependence dielectric permittivity shows typical Debye-type dielectric dispersion. Temperature-dependent DC resistivity shows that resistance decreases with the increase in temperature and follows Arrhenius behaviour in different temperature regions.     

Sensing properties of polyoxomolybdate doped polyaniline nanomaterials for oxidising and reducing volatile organic compounds

The polyoxomolybdates encapsulated PAni hybrid materials are prepared by interfacial polymerisation. In P12MPA, the crystal structure of 12MPA is not modified on doping with PAni. However, P11MPA have the polycrystallinity due to the presence of vanadium in the dopant molecule. Though, the hybrids prepared by interfacial polymerisation are in emaraldine salt form, there is a blue shift in the absorption spectra due to dopant induced decrease in conjugation length and over-oxidation. Interfacially polymerised PAniPOM hybrid materials are exposed with various concentrations of vapours of different volatile organic compounds (VOC) such as acetone, methanol, chloroform and carbon tetrachloride. The oxidising VOCs like acetone and methanol on exposure to PAni decrease the resistivity by hydrogen bonding with the redox cites of the polymer. Among these two, the sensitivity towards acetone is more in PAni and its hybrids which can be linked with the vapour pressure of the analyte. Due to the weak acidic characteristics of chlorinated hydrocarbons which are reducing vapours, the resistivity of PAni and its hybrids increases on exposure to chloroform and CCl4. Here, the chlorinated hydrocarbons interact with the redox sites of PAni and reduce it to base form. Bridging of polymer chains is also proposed for the reduction of conductivity on exposure to the analyte. The sensitivity is higher for the reducing analytes than that of the oxidising one.     

The pressure induced insulator to metal transition in FeSb2

The evolution of the ground state properties of FeSb(2) has been investigated via temperature (4.2-300 K), magnetic field (0-12 T) and pressure (0-8.8 GPa) dependent electrical resistivity studies. The temperature dependence of the resistivity follows activated behavior in the high temperature (HT) regime (T > 60 K), while variable range hopping (VRH) dictates the transport in the intermediate temperature (IT) regime (10 K > T > 45 K) and power law behavior is observed in the low temperature (LT) regime (T < 10 K). The pressure profoundly affects the resistivity in all the temperature regimes. The energy gap (Δ) extracted in the HT regime initially increases with pressure and then decreases, while the VRH parameter T(0) deduced in the IT regime is seen to decrease monotonically and vanish beyond 5 GPa leading to an insulator to metal transition (MIT) on account of delocalization of the electronic states in the gap. The analysis of the logarithmic derivative of the conductivity indicates the MIT to occur at ~6 GPa. The magnetoresistivity is found to be positive. The analysis of the resistivity behavior under pressure and magnetic field indicates that the former induces delocalization, while the latter tends to assist localization of the defect states inside the gap of FeSb(2).     

Role of mesoscopic morphology in charge transport of doped polyaniline

In doped polyaniline (PANI), the charge transport properties are determined by mesoscopic morphology, which in turn is controlled by the molecular recognition interactions among polymer chain, dopant and solvent, Molecular recognition plays a significant role in chain conformation and charge delocalization. The resistivity of PANI doped by camphor sulfonic acid (CSA)/2-acrylo-amido-1-propane sulfonic acid (AMPSA)/dodecyl benzene sulfonic acid (DBSA) is around 0.02 Ω cm. PANI-CSA and PANI-AMPSA show a metallic positive temperature coefficient of resistivity above 150 K. with a finite value of conductivity at 1.4 K; whereas, PANI-DBSA shows hopping transport at low temperatures. The magnetoresistance is positive (negative) for PANI-CSA (PANI-AMPSA); and PANI-DBSA has a large positive MR. The behavior of MR suggests subtle variations in mesoscopic morphology between PANI-CSA and PANI-AMPSA.     

Electrical and optical investigation on doping of II–VI compounds using radioactive isotopes

Using radioactive isotopes of shallow dopants (Ag, As, Rb) as well as of native or isoelectronic elements (Se, Te, Cd, Sr) which were incorporated as host atoms and then transmuted into relevant dopants (transmutation doping) we investigated doping phenomena occurring in the wide band gap II–VI compounds CdTe, ZnTe, ZnSe and SrS by the classical methods of semiconductor physics: Hall effect, C–V and photoluminescence measurements. Thus, we could assign unambiguously defect features in electrical and photoluminescence measurements to extrinsic dopants by means of the half lives of radioactive decay. In As doped ZnSe samples we observed two states: a metastable effective mass like state and a deep state. The occurrence of the latter state is always linked with the high resistivity of As doped ZnSe crystals. The transmutation doping experiments reveal that the so-called self-compensation typical for wide band gab II–VI compounds can be overcome when the thermal treatment for dopant incorporation is time separated from its electrical activation, achieved using transmutation at room temperature. Under these conditions we found an almost one-to-one doping efficiency relative to the implanted dose. Thus, these investigations are a contribution to understanding compensation phenomena occurring due to interactions between dopants and native defects during conventional doping treatments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of B-site isovalent doping on electrical and ferroelectric properties of lead free bismuth titanate ceramics

In the present work, zirconium modified bismuth titanate ceramics have been studied as potential lead-free ferroelectric materials over a broad temperature range (RT – 800 °C). Polycrystalline samples of Bi₄Ti_3−xZr_xO₁₂ (x=0.2, 0.4, 0.6) (BZrT) with high electrical resistivity were prepared using the solution combustion technique. The effect of Zr doping on the crystalline structure, ferroelectric properties and electrical conduction characteristics of BZrT ceramics were explored. Addition of zirconium to bismuth titanate enhances its dielectric constant and reduces the loss factor as it introduces orthorhombic distortion in bismuth titanate lattice which is exhibited by the growth along (0010) lattice plane. Activation energy due to relaxation is found to be greater than that due to conduction thus confirming that electrical conduction in these ceramics is not due to relaxation of dipoles. Remanent polarization of the doped samples increases as the Zirconium content increases.     

Synthesis and properties of boron doped ZnO nanorods on silicon substrate by low-temperature hydrothermal reaction

Boron doped ZnO nanorods were fabricated by hydrothermal technique on silicon substrate covered with a ZnO seed layer. It is found that the concentration of boric acid in the reaction solution plays a key role in varying the morphology and properties of the products. The growth rate along the [0 0 0 1] orientation (average size in diameter) of the doped ZnO nanorods decreased (increased) with the increase of boric acid concentration. Based on the results of XRD, EDX and XPS, it is demonstrated that the boron dopants tend to occupy the octahedral interstice sites. The photoluminescence of the ZnO nanorods related to boron doping are investigated.