Pulsed Electric Current Sintering of Silicon Nitride

Pulsed electric current sintering (PECS) has been used to densify α-Si₃N₄ powder doped with oxide additives of Y₂O₃ and Al₂O₃. A full density (>99%) was achieved with virtually no transformation to β-phase, resulting in a microstructure with fine equiaxed grains. With further holding at the sintering temperature, the α-to-β phase transformation took place, concurrent with an exaggerated grain growth of a limited number of elongated β-grains in a fine-grained matrix, leading to a distinct bimodal grain size distribution. The average grain size was found to obey a cubic growth law, indicating that the growth is diffusion-controlled. In contrast, the densification by hot pressing was accompanied by a significant degree of the phase transformation, and the subsequent grain growth gave a broad normal size distribution. The apparent activation energy for the phase transformation was as high as 1000 kJ/mol for PECS, almost twice the value for hot pressing (∼500 kJ/mol), thereby causing the retention of α-phase during the densification by PECS.     

Fabrication of integrated arrays of ultrahigh density magnetic nanowires on glass by anodization and electrodeposition

Integrated nanowire arrays of Fe-Pt, Co-Pt, and Ni-Pt alloys were successfully fabricated on glass substrates by successive anodization and electrodeposition. Porous alumina films, which were formed from an aluminum layers sputter-deposited on glass substrates covered with transparent oxide conductive films, were used as template-electrodes to deposit various magnetic alloys (Fe-Pt, Co-Pt, and Ni-Pt) in the nanopores by a cathodic electrodeposition, thus leading to integrated nanowire arrays with ultrahigh densities of (0.6-2.1) × 10¹⁵ wire m⁻². The as-deposited nanowires of Fe-Pt, Co-Pt, and Ni-Pt alloys are polycrystalline and composed of fine crystals (4-7 nm across) of chemically ordered tetragonal FePt, CoPt, or NiPt phase. The integrated nanowire arrays may be the promising candidate materials for ultrahigh density perpendicular magnetic recording media in terabits per square inch regime, due to the predictable enhanced perpendicular magnetic performance after appropriate annealing.     

Synthesis of γ-Ga2O3-Al2O3 solid solutions by spray pyrolysis method

Synthesis of the γ-Ga₂O₃-Al₂O₃ solid solutions by spray pyrolysis was examined. Spherical particles were obtained using an aqueous solution of Al(NO₃)₃ and Ga(NO₃)₃ with HNO₃. For Ga-rich composition, γ-phase solid solutions were directly crystallized by the spray pyrolysis. For Al-rich composition, spray pyrolysis gave amorphous products unless a sufficient thermal energy was supplied during the spray pyrolysis. Subsequent calcination of the amorphous products gave γ-Ga₂O₃-Al₂O₃ solid solutions. However, physical properties of the solid solutions were affected by the spray pyrolysis conditions.     

Intrinsic Elastic, Dielectric, and Piezoelectric Losses in Lead Zirconate Titanate Ceramics Determined by an Immittance-Fitting Method

The material coefficients of "soft" and "hard" lead zirconate titanate (PZT) ceramics were determined as complex values by the nonlinear least-squares-fitting of immittance data measured for length-extensional bar resonators. The piezoelectric d -constant should be a complex value to obtain a best fitting between observed and calculated results. Because the elastic, dielectric, and piezoelectric losses determined in this process were not "intrinsic" losses, a calculation process to evaluate the "intrinsic" losses was proposed. It was confirmed that the intrinsic losses were smaller than the corresponding extrinsic losses. The intrinsic piezoelectric loss existed in both soft and hard PZTs; ∼50% of the loss of piezoelectric d -constant was derived from the elastic and dielectric losses. The most notable difference between the soft and hard PZTs was observed in their elastic losses.     

Silver(I)-Ion-Mediated Cytosine-Containing Base Pairs: Metal Ion Specificity for Duplex Stabilization and Susceptibility toward DNA Polymerases

Spectroscopic characterization of Ag^I-ion-mediated C-Ag^I-A and C-Ag^I-T base pairs found in primer extension reactions catalyzed by DNA polymerases was conducted. UV melting experiments revealed that C-A and C-T mismatched base pairs in oligodeoxynucleotide duplexes are specifically stabilized by Ag^I ions in 1:1 stoichiometry in the same manner as a C-C mismatched base pair. Although the stability of the mismatched base pairs in the absence of Ag^I ions is in the order C-A≈C-T>C-C, the stabilizing effect of Ag^I ions follows the order C-C>C-A≈C-T. However, the comparative susceptibility of dNTPs to Ag^I-mediated enzymatic incorporation into the site opposite templating C is dATP>dTTP≫dCTP, as reported. The net charge, as well as the size and/or shape complementarity of the metal-mediated base pairs, or the stabilities of mismatched base pairs in the absence of metal ions, would be more important than the stability of the metallo-base pairs in the replicating reaction catalyzed by DNA polymerases.     

Fabrication and piezoelectric properties of BaTiO3/BaTiO3-Bi(Mg1/2Ti1/2)O3-BiFeO3 composites

We fabricated xBaTiO₃ (BT)/(1-x)[BaTiO₃-Bi(Mg_1/2Ti_1/2)O₃-BiFeO₃] (BT-BMT-BF)?+?0.1?wt%MnCO₃ composites by spark plasma sintering and investigated the effect of BT content x, BT powder size, and BT-BMT-BF composition on piezoelectric properties. For xBT/(1-x)(0.3BT-0.1BMT-0.6BF) +?0.1?wt%MnCO₃ (x?=?0–0.75) composites with a 0.5-µm BT powder, the dielectric constant was increased with x, and the relative density was decreased at x?=?0.67 and 0.75, creating optimum BT content of x?=?0.50 with a piezoelectric constant d₃₃ of 107?pC/N. When a larger 1.5-µm BT powder was utilized for the composite with x?=?0.50, the d₃₃ value increased to 150?pC/N due to the grain size effect of the BT grains. To compensate for a compositional change from the optimum 0.3BT-0.1BMT-0.6BF due to partial diffusion between the BT and 0.3BT-0.1BMT-0.6BF grains, a 0.5BT/0.5(0.275BT-0.1BMT-0.625BF)?+?0.1?wt%MnCO₃ composite with the 1.5-µm BT powder was fabricated. We obtained an increased d₃₃ value of 166?pC/N. These results provided a useful composite design to enhance the piezoelectric properties.     

Isotope scrambling in the formation of cyanopolyynes by laser ablation of carbon particles in liquid acetonitrile

Cyanopolyynes, H(CC)_nCN (n = 3–6), were formed by laser ablation of carbon particles in liquid acetonitrile. The molecules were separated according to the size n and characterized by UV absorption spectroscopy, mass spectroscopy in combination with gas-chromatographic separation, and nuclear magnetic resonance (NMR) spectroscopy. For the study of nascent carbon cluster distribution during the growth of the long carbon chain molecules, isotopomer distribution was analyzed by NMR spectroscopy for the product molecules. Two cyanopolyynes of HC₇N and HC₉N were isolated from solutions after laser ablation of isotope-enriched carbon powder (99% ¹³C) in liquid acetonitrile, CH₃CN, of natural isotopic abundance (1.1% ¹³C). With the observed chemical shift, δ, and spin–spin coupling constants, J_CH and J_CC, spectral simulation was made to determine relative abundance of possible isotopomeric forms for HC₉N. We found that the isotope of ¹²C, mostly from solvent molecules, contributes substantially for the part of carbon in the cyano group, –CN, in HC₉N. The isotopomer distribution observed for the sequence of H–CC–CC– was fairly explainable by a binomial, random distribution of the two carbon isotopes of ¹²C and ¹³C, reducing the concentration of ¹³C to 76–55%.     

Preparation of Mn2+-Cu+ co-doped P2O5–ZnO–Al2O3 glasses and their red fluorescence properties

To make a Mn²⁺-doped red glass phosphor that can be excited with ultraviolet (UV) light of light-emitting diodes (LEDs), 60P₂O₅-35ZnO-5Al₂O₃-8MnO-xCu₂O glasses (x = 0-1.00) were prepared by a melt-quenching method at 1200-1400°C for 30-180 minutes in atmospheric air, and the redox of Mn and Cu as well as fluorescence properties were investigated. The Mn²⁺ ion was not reduced and oxidized in the melting, quenching, and annealing processes. The valence of Cu in the glasses changed in the order of 0, 1+, and 2+ with the increase in the amount of Cu₂O and in the melting temperature and time. In this study, a 60P₂O₅-35ZnO-5Al₂O₃-8MnO-0.10Cu₂O glass melted at 1250°C for 90 minutes, having the highest Cu⁺ concentration, showed the strongest Mn²⁺ red fluorescence under the UV light at 275 nm. This strong Mn²⁺ red fluorescence has been caused by the energy transfer from excited Cu⁺ ions to Mn²⁺ ions.     

Factors affecting the generation of stress-assisted two-way memory effect in NiTi shape memory alloy

The combined effects of martensite pre-deformation and constrained stress on the generation of stress-assisted two-way memory effect (SATWME) were studied. Particular attention was paid to the generation of internal stress during thermal cycling under constant stress. The result highlights that the maximum SATWME is not determined solely by the maximum internal stress developed. The SATWME strain when subjected to 18% martensite pre-strain coincides, independently of constrained stress applied and internal stress developed. This study also provides experimental evidence that when under 400 MPa constrained stress the maximum SATWME shifts toward higher pre-deformation amplitude and this phenomenon is comparable to the increased cold-work. The results further suggest that the mechanism that associates with the change of M_s temperature plays critical role in determining the SATWME.