Thermoelectric Properties of Mo<Subscript>3</Subscript>Sb<Subscript>5.4</Subscript>Te<Subscript>1.6</Subscript> and Ni<Subscript>0.06</Subscript>Mo<Subscript>3</Subscript>Sb<Subscript>5.4</Subscript>Te<Subscript>1.6</Subscript>

Mo₃Sb₇, crystallizing in the Ir₃Ge₇ type structure, has poor thermoelectric (TE) properties due to its metallic behavior. However, by a partial Sb-Te exchange, it becomes semiconducting without noticeable structure changes and so achieves a significant enhancement in the thermopower with the composition of Mo₃Sb₅Te₂. Meanwhile, large cubic voids in the Mo₃Sb₅Te₂ crystal structure provide the possibility of filling the voids with small cations to decrease the thermal conductivity by the so-called rattling effect. As part of the effort to verify this idea, we report herein the growth as well as measurements of the thermal and electrical transport properties of Mo₃Sb_5.4Te_1.6 and Ni_0.06Mo₃Sb_5.4Te_1.6.     

Thermoelectric Properties of the One-Dimensional Cobalt Oxide CaCo<Subscript>2</Subscript>O<Subscript>4</Subscript>

In this work we studied the crystal structure and physical properties of the new one-dimensional cobalt oxide CaCo₂O_4+δ . The CaCo₂O_4+δ phase crystallizes as a calcium-ferrite-type structure, which consists of a corner- and edge-shared CoO₆ octahedron network including one-dimensional double chains. The specific-heat Sommerfeld constant γ was found to be 4.48(7) mJ/mol K². This result suggests that the CaCo₂O_4+δ phase has a finite density of states at the Fermi level. Metallic temperature dependence of the Seebeck coefficient S with a large thermoelectric power (S = 151 μV/K at 387 K) was observed. The origin of the large thermoelectric power may be attributed to the quasi one-dimensional character of the energy band near the valence band maximum in CaCo₂O_4+δ .     

Synthesis,Crystal Structure,and Transport Properties of Na<Subscript>22</Subscript>Si<Subscript>136</Subscript>

The type II clathrate Na₂₂Si₁₃₆ is prepared by the thermal decomposition of NaSi. Thermal analysis indicates this phase is metastable yet has a relatively high decomposition temperature. Rietveld analysis indicates that Na in the larger Si₂₈ cage is shifted off-center, analogous to observations in some type I clathrates. Temperature-dependent electrical and thermal transport properties are reported for Na₂₂Si₁₃₆, for which the spark plasma sintering technique was found to be effective in achieving intergrain sintering in the consolidated specimen. The potential that type II clathrate materials possess for thermoelectric applications is discussed.     

Superconducting and Transport Properties of (Bi-Pb)-Sr-Ca-Cu-O with Nano-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Additions

The effect of nano Cr₂O₃ additions in (Bi, Pb)-Sr-Ca-Cu-O superconductors using the coprecipitation method is reported. Nano Cr₂O₃ with 0.1, 0.3, 0.5, 0.7, and 1.0 wt.% were added to the (Bi, Pb)-Sr-Ca-Cu-O system. The critical temperature (T _c) and transport critical current density (J _c) were determined by the four-point probe technique. The phases in the samples were determined using the powder X-ray diffraction method. The microstructure was observed by a scanning electron microscope and the distribution of nano Cr₂O₃ was determined by energy-dispersive X-ray analysis (EDX). The maximum T _c and J _c were observed for the sample with 0.1 wt.% nano Cr₂O₃. The variation in the J _c of all the samples was explained by the effective flux pinning by nano Cr₂O₃ in the samples. Using the self-field approximation together with the dependence of J _c on temperature, the characteristic length (L _c) associated with the pinning force was estimated to be approximately the same as the average grain size in all the samples.     

First-Principles Study of Electronic Structure,Mechanical, and Thermoelectric Properties of Ternary Palladates CdPd<Subscript>3</Subscript>O<Subscript>4</Subscript> and TlPd<Subscript>3</Subscript>O<Subscript>4</Subscript>

Ternary palladates CdPd₃O₄ and TlPd₃O₄ have been studied theoretically using the generalized gradient approximation (GGA), modified Becke–Johnson, and spin–orbit coupling (GGA–SOC) exchange–correlation functionals in the density functional theory (DFT) framework. From the calculated ground-state properties, it is found that SOC effects are dominant in these palladates. Mechanical properties reveal that both compounds are ductile in nature. The electronic band structures show that CdPd₃O₄ is metallic, whereas TlPd₃O₄ is an indirect-bandgap semiconductor with energy gap of 1.1 eV. The optical properties show that TlPd₃O₄ is a good dielectric material. The dense electronic states, narrow-gap semiconductor nature, and Seebeck coefficient of TlPd₃O₄ suggest that it could be used as a good thermoelectric material. The magnetic susceptibility calculated by post-DFT treatment confirmed the paramagnetic behavior of these compounds.     

Fluxon pinning in the nodeless pairing state of superconducting YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript>

Positive-muon spin rotation (μ+SR) spectroscopy and magnetic moment measurements were used to probe fluxon (or vortex) formation in the superconducting mixed state of a high-purity YBa₂Cu₃O₇ crystal. Random potentials caused by crystal-lattice defects pin fluxons. A fluxon lattice forms in an external magnetic field, and changes of thermal activation lead to fluxon pinning and depinning. The root second moment of the local magnetic field distribution (σ) determined by μ+SR contains information on the magnetic penetration depth and the pinning. Fluxon pinning leads to temperature-dependent transverse displacements of the fluxons that decrease σ and also fluctuations in the separation between fluxons that tend to increase σ. By accounting for the field-dependent and temperature-activated fluxon disorder, it is found that the experimental results for the penetration depth are consistent with a supercon-ducting order parameter of a strong-coupling two-fluid model, confirming that the superconductivity is nodeless with s-wave superconducting pairing. Quantitative results for fluxon displacements are discussed within the context of the fluxon field-temperature phase diagram.     

Microwave Dielectric Properties of ZnO-2TiO<Subscript>2</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> Ceramics with BaCu (B<Subscript>2</Subscript>O<Subscript>5</Subscript>) Addition

The influence of BaCu(B₂O₅) (BCB) addition on the sintering temperature and microwave dielectric properties of ZnO-2TiO₂-Nb₂O₅ (ZTN) ceramic has been investigated using dilatometry, x-ray diffraction, scanning electron microscopy, and microwave dielectric measurements. A small amount of BCB addition to ZTN can lower the sintering temperature from 1100°C to 900°C. The reduced sintering temperature was attributed to the formation of the BCB liquid phase. The ZTN ceramics containing 3.0 wt.% BCB sintered at 900°C for 2 h have good microwave dielectric properties of Q × f = 19,002 GHz (at 6.48 GHz), ε _r = 45.8 and τ _f  = 23.2 ppm/°C, which suggests that the ceramics can be applied in multilayer microwave devices, provided that Ag compatibility exists.     

Growth of Polarity-Controlled ZnO Films on (0001) Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The polarity control of ZnO films grown on (0001) Al₂O₃ substrates by plasma-assisted molecular-beam epitaxy (P-MBE) was achieved by using a novel CrN buffer layer. Zn-polar ZnO films were obtained by using a Zn-terminated CrN buffer layer, while O-polar ZnO films were achieved by using a Cr₂O₃ layer formed by O-plasma exposure of a CrN layer. The mechanism of polarity control was proposed. Optical and structural quality of ZnO films was characterized by high-resolution X-ray diffraction and photoluminescence (PL) spectroscopy. Low-temperature PL spectra of Zn-polar and O-polar samples show dominant bound exciton (I₈) and strong free exciton emissions. Finally, one-dimensional periodic structures consisting of Zn-polar and O-polar ZnO films were simultaneously grown on the same substrate. The periodic inversion of polarity was confirmed in terms of growth rate, surface morphology, and piezo response microscopy (PRM) measurement.     

Protein-Assembled Nanocrystal-Based Vertical Flash Memory Devices with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Integration

This work presents vertical flash memory devices with protein-assembled PbSe nanocrystals as a floating gate and Al₂O₃ as a control oxide. The advantage of a vertical structure is that it improves cell density. Protein assembly improves uniformity of nanocrystals, which reduces threshold voltage variation among devices. The introduction of Al₂O₃ as a control oxide provided lower voltage/faster operation and hence less power consumption compared with the devices fabricated with SiO₂. The integration of Al₂O₃ appeared to be compatible with the protein assembly approach. In conclusion, Al₂O₃ has the potential to become the high-k control oxide due to its relatively high electron/hole barrier heights, and high permittivity.     

Indium- and tungsten-doped ZnGa<Subscript>2</Subscript>O<Subscript>4</Subscript> phosphor

This paper describes the optical characteristics of indium- and tungsten-doped ZnGa₂O₄ phosphor for field emission display (FED). The solid-state reaction is used to synthesize the phosphor powder, and the phosphor film is prepared by electrophoresis. Indium doping enhances the luminescence of ZnGa₂O₄ phosphor; nevertheless, the emission of phosphor doped by tungsten shifts to the short wavelength region. From the measurement of the cathodoluminescence (CL), it reveals that the luminescence of the phosphor film is improved when it is annealed in an O₂/Ar atmosphere. A luminance of 2,080 cd/m² is obtained as the phosphor film is excited at an electron voltage of 5 kV and an anode current of 30 μA.     

How r-Plane Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Surface Modifications Impact the Growth of Epitaxial (001) CeO<Subscript>2</Subscript> Thin Films

We present evidence that it is the presence or absence of atomic terraces with a specific crystallographic orientation on the (102) Al₂O₃ surface that promotes growth of single-crystal (001) CeO₂ films over polycrystalline (111) CeO₂ films. The CeO₂ film nucleates so that the [010] and [100] directions of the film align parallel and perpendicular to the terrace edges. In the absence of terraces, multidomain (111) CeO₂ films result in which the in-plane orientation of the two domains are rotated by 85.71°, so that a [110] CeO₂ direction aligns parallel to either the or Al₂O₃ direction.     

Structure and dielectric properties of Ba<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>ZnTi<Subscript>7</Subscript>O<Subscript>16</Subscript> hollandite ceramics

Hollandite-type Ba_1−xSr_xZnTi₇O₁₆ (x=0, 0.2, 0.4, 0.6, 0.8, and 1) ceramics have been synthesized by the conventional solid-state ceramic route. The phase purity and microstructure of these compositions have been characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis shows that an increase in strontium concentration in the A-site causes pairing of vacant tunnel sites, and hence the structure becomes unstable due to the collapse of the tunnel walls. The dielectric properties such as dielectric constant (ε_r), loss tangent (tan δ), and temperature variation of dielectric constant (τε_r) have been measured up to the 13 MHz region. The present study shows that zinc hollandites have relatively high dielectric constant and low loss tangent. The temperature variation of dielectric constant studies reveal that Ba-rich compositions have high positive τε_r and Sr-rich compositions have high negative τε_r in the 0–100°C region. Proper tailor making of these compositions has been attempted to arrive at near-zero temperature variation of the dielectric constant.     

Structure and Spectral Dependences of the Raman Scattering of Photosensitive CuIn<Subscript>0.95</Subscript>Ga<Subscript>0.05</Subscript>Se<Subscript>2</Subscript> Films on Glass,Aluminum, and Nanoporous Al/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Substrates

Photosensitive polycrystalline CuIn_0.95Ga_0.05Se₂ thin films have been formed on glass, aluminum, and nanoporous Al/Al₂O₃ substrates by means of two-step selenization in a gas (nitrogen) flow carrying a reaction component (selenium). The structural properties and the Raman scattering spectral dependences have been investigated. The dependence of the main lattice parameters and intensities of the Raman scattering lines on the substrate material is demonstrated.     

Density-Functional Study of the Electronic Structure and Optical Properties of Transparent Conducting Oxides In<Subscript>4</Subscript>Sn<Subscript>3</Subscript>O<Subscript>12</Subscript> and In<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript>

The electronic structure and optical properties of In₄Sn₃O₁₂ and In₄Ge₃O₁₂ are studied by the projector-augmented-wave method based on the density-functional theory within the generalized gradient approximation. The cation ordering of the two compounds is explored by means of first-principles calculations. It is found that the valence-band maximum of the materials is determined by the d states of metal elements and O-2p states; the conduction-band minimum is occupied by an admixture of the O-2p states, In-5s states, and Sn-5s or Ge-4s states, respectively. The two compounds are direct-bandgap semiconductors. The low intensity of the absorption coefficient, reflectivity, and loss function shows that they are good transparent conducting oxides.     

Er<Subscript>2</Subscript>O<Subscript>3</Subscript> for high-gain waveguide amplifiers

Following the demonstration of room-temperature luminescence, Er₂O₃ has been explored as a high-gain medium for ultra-compact waveguide amplifiers. With sputtered and annealed films, we measure three radiative lifetimes (7 ms, 0.8 ms, and 0.5 ms) and upconversion coefficients at 4.2 K. We have correlated these measurements with three crystalline phases: the thermodynamically stable bcc phase and the metastable fcc and hcp phases. The 7-ms lifetime is correlated with the fcc phase, implying the metastable crystal state has a profound influence on inhibiting upconversion interaction between neighbor Er atoms. Measurements indicate optical gain >3 dB/cm is possible.     

Effect of Proton Irradiation on Interface State Density in Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/GaN and Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/MgO/GaN Diodes

Proton irradiation of Sc₂O₃/GaN and Sc₂O₃/MgO/GaN metal-oxide semiconductor diodes was performed at two energies, 10 MeV and 40 MeV, and total fluences of 5 × 10⁹ cm⁻², corresponding to 10 years in low-earth orbit. The proton damage causes a decrease in forward breakdown voltage and a flat-band voltage shift in the capacitance-voltage characteristics, indicating a change in fixed oxide charge and damage to the dielectric. The interface state densities after irradiation increased from 5.9 × 10¹¹ cm⁻² to 1.03 × 10¹² cm⁻² in Sc₂O₃/GaN diodes and from 2.33 × 10¹¹ to 5.3 × 10¹¹ cm⁻² in Sc₂O₃/MgO/GaN diodes. Postannealing at 400°C in forming gas recovered most of the original characteristics but did increase the interfacial roughness.     

Destruction of an orbitally ordered and spin-polarized state: Colossal magnetoresistance in Ca<Subscript>3</Subscript>Ru<Subscript>2</Subscript>O<Subscript>7</Subscript>

The Ca₃Ru₂O₇ with a Mott-like transition at 48 K and a Neel temperature at 56 K features different in-plane anisotropies of magnetization and magnetoresistance. Applying the magnetic field along the magnetic easy axis precipitates a spin-polarized state via a first-order metamagnetic transition but does not lead to full suppression of the Mott state, whereas applying a magnetic field along the magnetic hard axis does, causing a resistivity reduction of three orders of magnitude. The colossal magnetoresistivity is attributed to the collapse of a novel, orbitally ordered and spin-polarized state. This new phenomenon is striking in that the spin polarization, which is a fundamental driving force for all other magnetoresistive systems, is detrimental to the colossal magnetoresistance (CMR) in this 4d-based electron system. Evidence for a density wave is also presented.     

Modified submicron luminescent materials based on the Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu and Y<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Eu polycrystals for full-color video-imaging devices and light sources

Modifying the polycrystalline phosphors Y₂O₃:Eu and Y₂O₂S:Eu in order to allow their application as submicron composite materials for electrovacuum luminescent video-imaging devices and light sources is considered. The effect of synthesizing such materials through the use of H₃BO₃ on their crystal structure, spectral characteristics, and photo- and cathodoluminescence intensities is investigated.     

Fabrication and Electromagnetic Properties of Conjugated NH<Subscript>2</Subscript>-CuPc@Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>

Conjugated amino-phthalocyanine copper containing carboxyl groups/magnetite (NH₂-CuPc@Fe₃O₄) has been fabricated from FeCl₃·6H₂O and NH₂-CuPc via a simple solvothermal method and its electromagnetic properties investigated. Scanning electron microscopy and transmission electron microscopy revealed that the NH₂-CuPc@Fe₃O₄ was a waxberry-like nanomaterial with NH₂-CuPc molecules effectively embedded in the interior of Fe₃O₄ particles in the form of beads. Introduction of NH₂-CuPc effectively improved the complementarity between the dielectric and magnetic losses of the system, resulting in excellent electromagnetic performance. The minimum reflection loss of the as-prepared composite reached ?33.4 dB at 7.0 GHz for coating layer thickness of 4.0 mm and bandwidth below ?10.0 dB (90% absorption) of up to 3.8 GHz. These results indicate that introduction of NH₂-CuPc results in a composite with potential for use as an electromagnetic microwave absorption material.     

Electronic Structure and Thermoelectric Properties of the Delafossite-Type Oxides CuFe<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript>

In this study, we investigated the chemical composition and electronic structure of the delafossite-type oxides CuFeO₂ (CFO) and CuFe_0.98Ni_0.02O₂ (CFNO). The hole carrier density in the Cu and FeO₂ layers of CFNO was found to be different from that of CFO, leading to the enhancement of electrical conductivity by Ni substitution. In addition, thermoelectric properties were found to be affected by the surface treatment, possibly due to some surface contamination. An etched CFNO (E-CFNO) exhibited a higher electrical conductivity and a higher Seebeck coefficient relative to the polished CFNO (P-CFNO). The thermal conductivity did not change much between E-CFNO and P-CFNO. As a result, the thermoelectric performance of E-CFNO was higher than that of P-CFNO. This result indicates that etching is needed when we use CFNO as a p-leg in thermoelectric generators.