Electrical conductivity of tetragonal stabilized zirconia

The electrical conductivity change on annealing for tetragonal stabilized zirconia (TZP) was studied with the help of a.c. impedance dispersion analysis techniques. The dependences of the conductivity on annealing time at 1000 ° C and on temperature cycling between room temperature and 1000 ° C were investigated. A decrease in conductivity of about 30% at 1000 ° C of TZP with 3 mol% Y₂O₃ was observed during the first 200 h of annealing at 1000 ° C, and no change was observed during further annealing. A similar result was observed for TZP with 2.9 mol% Sc₂O₃. For TZP with 3.0mol% Yb₂O₃, the conductivity decreased gradually during an annealing time of over 2000 h. The impedance dispersion analysis at lower temperature suggested that the decrease in electrical conductivity by annealing at 1000 ° C could be attributed to the increases of both grain boundary and intragrain resistance. No monoclinic phase was observed for the samples annealed at 1000 ° C for 2000 h. On the other hand, a trace of a monoclinic phase was found for TZP with 3mol% Y₂O₃ after the 50th temperature cycling, but no significant decrease in conductivity was observed with the cycling.     

Ultrasonic study of sintered SiC at low temperatures

We investigated the temperature dependence, at low temperaturs, of sound velocity in sintered silicon carbide samples, containing three different sintering additives, boron or beryllium oxide or aluminum nitride. It was found that samples containing AlN or B showed lnT dependence (T is the temperature) of sound velocity but the one with BeO did not. The slope of the lnT dependence, which is proportional to the density of states of two level tunneling systems (TLS), is much larger for SiC with AlN than that with B. This sequence and no lnT dependence in BeO, correlate with the solubility of these additives into SiC, suggesting that the TLS, at least in this case, are created by the additives in solid solutions in the crystals. The samples containing B were heat treated to allow grain growth as well as densification. The density of states of TLS in these samples (measured by the slope of the lnT dependence of velocity) increased as the grain size increased. This suggests that the TLS do not reside in grain boundaries and that B migrates from the grain boundaries (where it originally segregated) into the bulk, thus creating more TLS inside the grains.     

Ubiquitous Memories: a memory externalization system using physical objects

In this paper we propose an object-triggered human memory augmentation system named “Ubiquitous Memories” that enables a user to directly associate his/her experience data with physical objects by using a “touching” operation. A user conceptually encloses his/her experiences gathered through sense organs into physical objects by simply touching an object. The user can also disclose and re-experience for himself/herself the experiences accumulated in an object by the same operation. We implemented a prototype system composed basically of a radio frequency identification (RFID) device. Physical objects are also attached to RFID tags. We conducted two experiments. The first experiment confirms a succession of the “encoding specificity principle,” which is well known in the research field of psychology, to the Ubiquitous Memories system. The second experiment aims at a clarification of the system’s characteristics by comparing the system with other memory externalization strategies. The results show the Ubiquitous Memories system is effective for supporting memorization and recollection of contextual events.     

Fluorescence EXAFS analysis of ErP grown on InP by organometallic vapor phase epitaxy using a new organometal Er(EtCp)3

We have investigated local structures of ErP grown by organometallic vapor phase epitaxy Er source: tris(ethylcyclopentadienyl)erbium (Er(EtCp)₃ by extended X-ray absorption fine structure (EXAFS) measurement. The EXAFS analysis revealed that NaCl-type ErP and Er–O(–C) compounds coexisted in the case of ErP growth by using Er(EtCp)₃. The NaCl-type ErP was preferentially formed on InP(1 1 1)A compared with InP(0 0 1) and InP(1 1 1)B. It is considered that formation of unexpected Er–O(–C) compounds is due to low but significant concentration of residual O and/or C in Er(EtCp)₃.     

Environmental protection: researches in National Institute of Radiological Sciences

Some studies for radiological protection of the environment have been made at the National Institute of Radiological Sciences (NIRS). Transfer of radionuclides and related elements has been investigated for dose estimation of non-human biota. A parameter database and radionuclide transfer models have been also developed for the Japanese environments. Dose (rate)-effect relationships for survival, growth and reproduction have been investigated in conifers, Arabidopsis, fungi, earthworms, springtails, algae, duckweeds, daphnia and medaka. Also genome-wide gene expression analysis has been carried out by high coverage expression profiling (HiCEP). Effects on aquatic microbial communities have been studied in experimental ecosystem models, i.e., microcosms. Some effects were detected at a dose rate of 1 Gy day(-1) and were likely to arise from interspecies interactions. The results obtained at NIRS have been used in development of frameworks for environmental protection by some international bodies, and will contribute to environmental protection in Japan and other Asian countries.     

Analysis of nonlinear transient responses of piezoelectric resonators

The electric transient response method is an effective technique to evaluate material constants of piezoelectric ceramics under high-power driving. In this study, we tried to incorporate nonlinear piezoelectric behaviors in the analysis of transient responses. As a base for handling the nonlinear piezoelectric responses, we proposed an assumption that the electric displacement is proportional to the strain without phase lag, which could be described by a real and constant piezoelectric e-coefficient. Piezoelectric constitutive equations including nonlinear responses were proposed to calculate transient responses of a piezoelectric resonator. The envelopes and waveforms of current and vibration velocity in transient responses observed in some piezoelectric ceramics could be fitted with the calculation including nonlinear responses. The procedure for calculation of mechanical quality factor Q(m) for piezoelectric resonators with nonlinear behaviors was also proposed.     

Effect of CO2 on layered Li1+zNi1−x−yCoxMyO2 (M = Al,Mn) cathode materials for lithium ion batteries

We investigated the effect of CO₂ on layered Li_1+zNi_1−x−yCo_xM_yO₂ (M = Al, Mn) cathode materials for lithium ion batteries which were prepared by solid-state reactions. Li_1+zNi_(1−x)/2Co_xMn_(1−x)/2O₂ (Ni/Mn mole ratio = 1) singularly exhibited high storage stability. On the other hand, Li_1+zNi_0.80Co_0.15Al_0.05O₂ samples were very unstable due to CO₂ absorption. XPS and XRD measurements showed the reduction of Ni³⁺ to Ni²⁺ and the formation of Li₂CO₃ for Li_1+zNi_0.80Co_0.15Al_0.05O₂ samples after CO₂ exposure. SEM images also indicated that the surfaces of CO₂-treated samples were covered with passivation films, which may contain Li₂CO₃. The relationship between CO₂-exposure time and CO₃²⁻ content suggests that there are two steps in the carbonation reactions; the first step occurs with the excess Li components, Li₂O for example, and the second with LiNi_0.80Co_0.15Al_0.05O₂ itself. It is well consistent with the fact that the discharge capacity was not decreased and the capacity retention was improved until the excess lithium is consumed and then fast deterioration occurred.