Hideyuki Kurosawa

Stabilized zirconia-based sensor using oxide electrode for detection of NOx in high-temperature combustion-exhausts

Abstract New type NOx sensors were newly designed by using stabilized zirconia and an oxide sensing electrode. Among the various oxides examined for the sensing electrode, CdMn2O4 was found to be the most excellent material. Both planar and tubular devices attached with a sputtered CdMn2O4 layer could respond well to NO2 as well as NO in air at higher temperature, such as 500 °C. The EMF values of the devices were almost linear to the logarithm of NOx concentration with a positive slope for NO2 and a negative slope for NO. A NOx sensing mechanism involving mixed potential was proposed based on the measurements of polarization curves.

Mixed potential type NO{sub x} sensor based on stabilized zirconia and oxide electrode

A new solid-state NO{sub x} sensor operative at high temperature was designed using stabilized zirconia and an oxide sensing electrode. Among the various oxides examined, CdMn{sub 2}O{sub 4} was found to be the most excellent material for NO{sub x} sensing at 500 C. The EMF values of the sensor were almost linear to the logarithm of NO{sub x} concentration with a positive slope for NO{sub 2} and a negative slope for NO. A nitrogen oxide sensing mechanism involving mixed potential was proposed based on the measurements of polarization curves.

Formation of Bismuth Strontium Calcium Copper Oxide Superconducting Films by Chemical Vapor Deposition

Superconducting films of bismuth strontium calcium copper oxides were prepared by chemical vapor deposition at 910?C and 1 Torr on MgO substrate using a bismuth alkoxide and ?-diketonate chelates of Sr, Ca and Cu as source materials. In the film with Tc(zero) of 78 K, the predominant phase was Bi2(Sr, Ca)3Cu2Ox with the c-axis perpendicular to the substrate.

Stabilized zirconia-based NOx sensor operative at high temperature

Abstract An electrochemical device combining an MgO-stabilized zirconia (MSZ) tube with an auxiliary phase of Ba(NO 3 ) 2 was found to exhibit fairly good Nernsts response to dilute NO 2 in air at elevated temperature (450 °C). The response to NO in air could be improved to be roughly comparable to that to NO 2 when Ba(NO 3 ) 2 was added with 10 mol% CaCO 3 . The EMF response of the tubular device to a fixed concentration of NO 2 or NO was strongly dependent on O 2 concentration. The effect of O 2 was much mitigated with a probe-type planar device.

Tc of c-Axis-Oriented Y-Ba-Cu-O Films Prepared by CVD

YBa2Cu3O7-x thin films (0.8 µm in thickness) with c-axis orientation were prepared at 900°C on yttria-stabilized zirconia substrates by chemical vapor deposition using metal chelates as source materials. The onset and completion of the superconductive transition occurred at 89 K and 80 K, respectively, for the film that received in situ oxygen treatment. The oxygen-treated film had metallic resistivity and the resistance ratio (R273 K / R100 K) was 2.

Preparation of Bi-Sr-Ca-Cu-O Superconducting Films by CVD

Bi-Sr-Ca-Cu-O (BSCCO) films were prepared on MgO(100) single-crystal substrates at 770°C by chemical vapor deposition using β-diketone metal chelates of Sr, Ca and Cu and Bi-triethoxide. The films were Bi2(Sr, Ca)3Cu2Ox (c=30 A) with c-axis orientation. The films showed superconducting transition onset at 90 K with zero resistivity at 74 K. The formation of films having high-Tc phase (Bi2(Sr, Ca)4Cu3Ox, c=37 A) was achieved when the films were annealed at 890°C for 5 h under 760 Torr of oxygen. The resistivity of the annealed films began to drop sharply at around 110 K and reached zero at 77 K.

Effect of deposition temperature on the superconducting properties of Y-Ba-Cu-O films prepared by CVD

Abstract The relationship between CVD deposition temperature and the resulting deposits crystallinity and superconducting characteristics was examined for Y-Ba-Cu-O films prepared on SrTiO3 (100) single-crystal substrates. The source materials used in the CVD process were β-diketone metal chelates. The crystallinity was evaluated from an integral width of a (007) X-ray diffraction peak of YBa2Cu3O7−x deposited at 600–900°C. The films deposited at 750–900°C showed not only a higher crystallinity level than that of the films deposited at 600–700°C but also exhibited superconductivity. The highest level of crystallinity, the highest zero-resistance (Tc = 91.5 K) and the highest critical-current density (3.9 × 105 A/cm2) at 77.3 K and 0 T were measured for the film deposited a 850°C. This film consisted of mostly c-axis oriented grains with a few a-axis oriented grains.

Critical Current Criterion in High-Tc Superconducting Films

Critical current densities at 77.3 K obtained by a voltage criterion of 2 µV/cm were 5.6×105 A/cm2 at 0 T and 3.1×104 A/cm2 at 27 T for the best Y1Ba2Cu3O7-δ film prepared by chemical vapor deposition. Current-voltage curves were fitted by a power law of the form V∝In with small n-values of 4–14. Since its n-value is 7 at 27 T, the Jc corresponds to 2.8×104 A/cm2 in the 1 µV/cm criterion and also to 2.0×104 A/cm2 in the 0.1 µV/cm one. In the critical current measurement for superconducting oxides, the n-value together with the criterion should always be described.

Preparation of a high-Jc Y-Ba-Cu-O film at 700 °C by thermal chemical vapor deposition

A high‐Jc Y‐Ba‐Cu‐O superconducting film was successfully prepared at 700 °C on a SrTiO3(100) single‐crystal substrate without postannealing by thermal chemical vapor deposition under a low‐oxygen partial pressure of 0.036 Torr in the total gas introduced into a hot‐wall‐type reactor (total gas pressure: 10 Torr), using 1% O2 balanced with Ar as a reactant gas. The sources for the elements of Ba, Y, and Cu were β‐diketone metal chelates. The film mainly consisted of YBa2Cu3Ox with c‐axis orientation perpendicular to the substrate plane and included small amounts of a‐axis oriented and randomly oriented grains. The film showed the superconducting transition temperature defined by zero resistivity at 89 K. The critical current density based on a 2 μV/cm criterion was 2.2 × 106 A/cm2 at 77.3 K and 0 T.

Low-Temperature Deposition of Y-Ba-Cu-O Superconducting Films by Thermal Chemical Vapor Deposition

Y-Ba-Cu-O superconducting films having a zero-resistance temperature of 84-85 K were prepared at 650°C on SrTiO3(100) single-crystal substrates without postannealing by thermal chemical vapor deposition using β-diketone metal chelates as sources and O2 with low partial pressure as a reactant gas. The films mainly consisted of YBa2Cu3Ox with a-axis and c-axis orientations normal to the film planes.