Soichi Ishihara

Crystal structure of corundum type Mg4(Nb2-xTax)O9 microwave dielectric ceramics with low dielectric loss

Abstract New microwave dielectric ceramics, i.e. Mg 4 (Nb 2− x Ta x )O 9 (MNT) solid solutions, were synthesized and their microwave dielectric properties and crystal structure were investigated in this study. From the discrete variational Xα (DV-Xα) method, it was found that the Ta–O bonds in the TaO 6 octahedron become more covalent than Nb–O bonds in the NbO 6 octahedron; this result leads to the decrease of the ionicity in the Ta 5+ ion. The dielectric constants of MNT were slightly decreased from 12.4 to 11.5; this result might be due to the covalent interaction of Ta–O bonding. The quality factors of the samples were found to exhibit high value ( Q · f ≒350 000 GHz for x =2) which is comparable to those of Al 2 O 3 .

Influence of Zn and Ni substitutions for Mg on dielectric properties of (Mg4-xMx)(Nb2−ySby)O9 (M=Zn and Ni) solid solutions

Abstract The effects of M substitution for Mg and Sb substitution for Nb in the (Mg 4− x M x )(Nb 2− y Sb y )O 9 ( M =Zn and Ni) ( x =0–2, y =0–1.5) solid solutions on the microwave dielectric properties were investigated in this study. The limits of both (Mg 4− x M x )Nb 2 O 9 ( M =Zn and Ni) solid solutions were approximately x =2, whereas that of Mg 4 (Nb 2− y Sb y )O 9 solid solutions was approximately y =1.5. As for the Ni and Zn substitutions for Mg, the quality factor, Q · f values of the (Mg 4− x M x )Nb 2 O 9 ( M =Zn and Ni) solid solutions decreased from 192 268 to 28 400GHz with increasing composition x from 0 to 2. On the other hand, the Q · f values of the Mg 4 (Nb 2− y Sb y )O 9 solid solutions were remarkably improved by the Sb substitution for Nb; the highest Q · f value of 285 423 GHz was obtained at y =1. It was found that an increase in the Q · f values of Mg 4 (Nb 2− y Sb y )O 9 solid solutions may related to the grain size decreased which is opposite to general results and this relation is consistent with that of Al 2 O 3 .

Effects of variations in crystal structure on microwave dielectric properties of Y2BaCuO5 system

Abstract The dielectric properties of (Y 2– x R x )BaCuO 5 ( R =Sm, Gd, Dy, Ho, Er and Tm) solid solutions were measured for the application as a new microwave resonator. Moreover, the relationships between the results of the dielectric properties obtained and variation in the crystal structure of (Y 2− x R x )BaCuO 5 solid solutions have been studied in some detail using the results of Reitveld analysis. The result is that e r changes from 12.7 to 19.6 and depend on the ionic radii of the rare-earth which composed the R 2 O 11 polyhedron. Then, τ f was largely improved by substituting R for Y, and in the case of Dy 2 BaCuO 5 compound, the value was −6.4ppm/°C. Using the results of Rietveld analysis obtained at 20 and 80 o C, negative values of τ e were considered to be caused by a decrease in the atomic distances of the R 2 O 11 polyhedron in the direction of the b -axis. As for the Q·f value, it suggests that the difference of Q·f value between x =1 and 2 is reduced by the strain of R 2 O 11 polyhedron which is caused by the difference of ionic radii of Y and R .

Microwave dielectric properties and crystal structure refinements in M (M=Sr, Ca) doped Nd2(Ba1–xMx)ZnO5 solid solutions

Abstract The microwave dielectric properties and crystal structure stability estimated by the bond valence sum of Nd 2 BaZnO 5 ( e r =22.6, τ f =4.6 ppm/°C, Q · f =12,451 GHz), Nd 2 Ba 0.5 Sr 0.5 ZnO 5 ( e r =25.5, τ f =26.0 ppm/°C, Q · f =6185 GHz) and Nd 2 Ba 0.5 Ca 0.5 ZnO 5 ( e r =26.4, τ f =24.0 ppm/°C, Q · f =6210 GHz) were evaluated in this study. It was clarified that substituting Sr or Ca for Ba induces the decrease of lattice parameters at Nd 2 Ba 0.5 Sr 0.5 ZnO 5 ( a =6.7391(4), c =11.4592(4) ) and Nd 2 Ba 0.5 Ca 0.5 ZnO 5 ( a =6.7386(4), c =11.4597(5) ) in comparison with those of Nd 2 BaZnO 5 ( a =6.7391(4), c =11.4592(4) ) and volume of BaO 10 polyhedron by Rietveld analysis. In this case, an instability in the crystal structure of Nd 2 Ba 0.5 Sr 0.5 ZnO 5 and Nd 2 Ba 0.5 Ca 0.5 ZnO 5 is induced by the bond valence difference between Ba and Sr or Ca ions. Our research that the crystal structure instability in particular influences a decrease of the Q · f value in this system.

Microwave Dielectric Properties and Crystal Structure of Y2(Ba1-xSrx)(Cu1-yZny)O5 Solid Solutions Synthesized by a Solid-State Reaction Method.

The microwave dielectric properties of Y2Ba0.7Sr0.3(Cu1-yZny)O5 (y=0 to 1) solid solutions have been discussed on the basis of the crystal structure refined by the Rietveld method. The variations in the lattice parameters depend on the changes in the atomic distances in an MO5 (M=Cu and/or Zn) pyramid with Zn substitution for Cu. In addition, it is recognized that these variations in the MO5 pyramid also exert on the variations in the atomic distances of an AO11 (A=Ba and/or Sr) polyhedron. The quality factor (Qf) of the microwave dielectric properties obtained in this study shows a maximum in the sample of Y2Ba0.7Sr0.3(Cu0.15Zn0.85)O5 solid solution, increasing with the increase of Zn content in the solid solutions, and the value is 23643 GHz. Thus, it was suggested that the Qf values are closely related to the variation in atomic distances of both AO11 polyhedra and MO5 pyramids.

Development of Air-Cooled Cylinder by Utilizing Natural Convection

An air-cooled engine with a finned cylinder may have residual heat between the fins. Residual heat decreases heat release from the cylinder when cooling air is not forced over the engine. In order to induce natural convection in the cylinder, cooling ports were drilled in the fins parallel to the cylinder axis to determine if residual heat could be decreased and additional cylinder cooling could be developed. The effects of the fin configurations on air-cooling were investigated to utilize the cooling ports for a stationary engine and a non-moving motorbike engine. The experimental cylinder design permitted variation in the number of fins and fin pitch. Numbers of fins that had various port sizes and port positions were investigated; in addition, the temperature inside of the cylinder and in the space between the fins was measured. Results indicated that heat release from the cylinder was increased by utilizing the fins with ports as compared to the fins without ports. It was also found that fin pitch, number of fins, port size, port position, and number of ports have significant effects on cylinder temperature. These results can be utilized to improve the design of an air-cooled cylinder by utilizing natural convection.

Crystal structure of Y2Ba(Cu1−xZnx)O5 (x=0 to 1) solid solutions

Abstract A new material for use as a microwave resonator was developed by evaluating the microwave dielectric properties of Y 2 Ba(Cu 1− x Zn x )O 5 solid solutions. The details on the crystal structure of Y 2 Ba(Cu 1− x Zn x )O 5 solid solutions were studied by using X-ray powder diffration (XRPD) and these patterns were indexed. The results show that some peaks of the intensities were reversed as the quantities in Zn substitution for Cu were increased with an increase in composition x . It was concluded that these reverses in the peaks are induced by the variation in the lattice parameters.

Improvement of Pitot Tube Set for Obtaining Scavenging Pictures of Two-Stroke Cycle Engines

The scavenging picture means here the velocity distribution of the scavenging flow in the cylinder measured by a pitot tube. The picture is often used to investigate the suitability of the design of the scavenging system in a two-stroke cycle engine. In measurements by pitot tube only the upward component of the velocity has been measured until now. By this improvement, however, it is well possible to measure the velocity in three dimensions. In other words, it is now possible to measure also the scavenging flow toward the exhaust port after the flow turns downward at the cylinder head.

Improvement of Michell Workshop Viscometer

The Michell viscometer is mainly composed of a cup and a ball. The viscosity is indicated by the time, during which the ball adheres to the cup against the gravity, after the space between them has been filled with oil sample and the ball has been pressed against the cup firmly. Although the mechanism of this viscometer is very simple and the viscosity can be measured using only several drops of the sample, it has not been used widely. The authors have improved this viscometer in several points and developed a constant temperature box for it. As a result, the reliability of the measurement has become higher and the operation of the viscometer easier. For example, we can know numerically the relation between the distance covered and the kinematic viscosity of automotive engine oil without any difficulties.