The thermoelectric properties of Magnèli phase titanium oxides Ti n O 2n−1 ͑n =2,3,...͒ have been investigated, paying special attention to how the thermoelectric performance can be altered by changing the microstructure. Dense polycrystalline specimens with nominal composition of TiO 2−x ͑x = 0.05, 0.10, 0.15, and 0.20͒ prepared by conventional hot-pressing are all identified to be one of the Magnèli phases, in which crystallographic shear planes are regularly introduced according to the oxygen deficiency. Electrical conduction is n-type for all specimens and the carrier concentration increases with the increase in the oxygen deficiency. The values of lattice thermal conductivity, on the other hand, decrease with the increase in the oxygen deficiency, which can be attributed to phonon scattering at the crystallographic shear plane. The largest value of thermoelectric figure of merit Z, 1.6ϫ 10 −4 K −1 was obtained at 773 K for the hot-pressed specimen of TiO 1.90 .

No abstract

The high-efficiency conversion of threading screw dislocations (TSDs) in 4H-SiC by solution growth provides an efficient method of obtaining ultra high-quality SiC crystals. The behavior of TSDs on on-axis and off-axis 4H-SiC{0001} seed crystals was investigated by synchrotron X-ray topography. Almost all TSDs in the off-axis Si-face seed crystal were converted to Frank-type stacking faults on the basal planes. The conversion ratio of TSDs was highly influenced by the surface polarity of the seed crystal. The stacking faults laterally propagate toward the outside of the crystal. #

Chiral symmetry breaking in NaClO3 crystallization from an aqueous solution with perturbations has been of great interest. To understand the mechanism, several models focusing on the early stage of the crystallization have been proposed. However, they are ambiguous because the early stage has been barely explored directly. Here, we investigate the early stages of the crystallization process driven by droplet evaporation using a combination of direct in situ microscopic observations and cryogenic single-crystal XRD experiments. We demonstrate that an achiral crystal having P21/a symmetry, which is newly discovered for a solution growth, first appears in the droplet and then transforms into the chiral crystals. Additionally, determination of the lattice constants by XRD experiments (a = 8.42 Å, b = 5.26 Å, c = 6.70 Å, β = 109.71°) revealed that the achiral phase should be identical to Phase III (a = 8.78 Å, b = 5.17 Å, c = 6.83 Å, β = 110°), which is a high-temperature phase from a melt growth of NaClO3. We advocate further assessment of the achiral crystal and a new pathway for the formation of chiral crystals via crystalline phase transition from achiral Phase III.

Scandium and yttrium co-doped barium zirconate ͓BaZr 0.85 Sc x Y 0.15-x O 3-␦ ͑x = 0, 0.05, 0.075, 0.10, 0.15͔͒ have been investigated in terms of phase relationship, microstructures, and electrical conductivity. The bulk conductivity of the scandium and yttrium co-doped barium zirconate increased with the dopant ratio of yttria. BaZr 0.85 Sc 0.05 Y 0.10 O 3-␦ had the highest grain-boundary conductivity among the scandium and yttrium co-doped barium zirconates in this study. But, BaZr 0.85 Sc 0.15 O 3-␦ , BaZr 0.85 Sc 0.10 Y 0.05 O 3-␦ , BaZr 0.85 Sc 0.75 Y 0.075 O 3-␦ , and BaZr 0.85 Sc 0.05 Y 0.10 O 3-␦ consisted of a single cubic perovskite phase at 1600°Cand their densities of grain-boundary were smaller than that of BaZr 0.85 Y 0.15 O 3-␦ . From the observation of microstructure and results of grain boundary-conductivity measurement, we can say that yttrium is a dopant that increases specific grain-boundary conductivity and bulk conductivity, and scandium is a dopant that increases the grain size. Thus, there is a trade-off relation between the grain size and specific grain-boundary conductivity based on the mixing ratio of scandia to yttria. The total conductivity of BaZr 0.85 Sc 0.05 Y 0.10 O 3-␦ at 600°C was estimated to be 1.6 ϫ 10 −2 S cm −1 , which is the highest-class conductivity among reported trivalent cation-doped barium zirconates.