Kumiko Kaneta

Ba(Mg1/3Ta2/3)O3 Ceramics with Temperature-Stable High Dielectric Constant and Low Microwave Loss

A dense ceramic with an ordered perovskite structure with chemical formula Ba(Mg1/3Ta2/3)O3 is prepared, aiming at materials for a dielectric resonator with temperature-stable high dielectric contsant and low loss at microwave frequency. A small amount of Mn ion is doped to the sample to complete the sintering. The dielectric constant and unloaded Q are 25 and 16800 at 10.5 GHz respectively. The temperature coefficient of resonant frequency is estimated as 2.7 ppm/°C in the vicinity of room temperature. The value of Q we obtained is the highest among those reported so far on ceramics having a similar characteristic.

Ba(Zn1/3Nb2/3)O3–Sr(Zn1/3Nb2/3)O3 Solid Solution Ceramics with Temperature-Stable High Dielectric Constant and Low Microwave Loss

Solid solution ceramics in the Ba(Zn1/3Nb2/3)O3(BZN)–Sr(Zn1/3Nb2/3)O3 (SZN) system have been studied with a view to finding materials for use as dielectric resonators at microwave frequency. The relative dielectric constant and the unloaded Q at 10 GHz are respectively 41 and 5400 for BZN, and 40 and 2000 for SZN. The temperature coefficient of the resonant frequency is estimated as 30 ppm/°C for BZN and -38 ppm/°C for SZN. The dielectric constant of 0.3 BZN–0.7 SZN ceramic is nearly independent of temperature, which gives a very small estimated temperature coefficient of the resonant frequency of -5 ppm/°C.

Effect of Mn Doping on the Dielectric Properties of Ba2Ti9O20 Ceramics at Microwave Frequency

The effect of Mn doping on the dielectric properties of Ba2Ti9O20 ceramics has been investigated at microwave frequency. The dielectric constant and the temperature coefficient are not sensitive to the addition of Mn, while the unloaded Q depends strongly upon it as well as on heat treatment at high temperature. A minute addition of Mn leads to an increase in the Q value. A high value of Q of more than 5200 was obtained at 9 GHz with the addition of 0.5~1.0 mol% Mn.

Phase transition in the PbTiO - A(B23Nb13)O3 (A = La, Bi; B = Zn, Mg) solid solutions

Abstract Phase transition in the (1− x ) PbTiO 3 - xA ( B 2 3 Nb 1 3 ) O 3 ( A = La, Bi ; B = Zn,Mg ) solid solution systems has been investigated by means of x-ray diffraction, dilatometric and dielectric measurements. Complete solid solutions with a perovskite structure are formed in the ranges of 0 PbTiO 3 - La ( B 2 3 Nb 1 3 ) O 3 and PbTiO 3 - Bi ( B 2 3 Nb 1 3 ) O 3 systems, respectively. The tetragonal distortion at room temperature decreases with increasing the La ( B 2 3 Nb 1 3 ) O 3 or Bi ( Mg 2 3 Nb 1 3 ) O 3 molar fraction, while it increases with the Bi ( Zn 2 3 Nb 1 3 ) O 3 content. The ferroelectric Curie temperature determined by the dielectric and/or dilatometric measurements decreases rapidly with the increase of the La ( B 2 3 Nb 1 3 ) O 3 content, but slightly decreases or increases with Bi compounds in the case of the Bi ( Mg 2 3 Nb 1 3 ) O 3 or Bi ( Zn 2 3 Nb 1 3 ) O 3 series, respectively.

Magnetic and Mössbauer studies of FeNi2BO5 and FeNiBO4

Abstract Single crystals of boron ferrites Fe III Ni II 2 BO 5 and Fe III Ni II BO 4 were grown by CVT method using HCl carrier gas. The measurements of magnetic susceptibility and Fe 57 Mossbauer effect were performed on the powdered samples in the temperature range from 4.2 K to 295K. FeNi 2 BO 5 (FeNiBO 4 ) exhibits antiferromagnetic transition at T N =54 K (13 K) giving asymptotic Curie temperature of −220 K (−900 K) and the Curie constant agrees well with what is expected from Fe 3+ and Ni 2+ ions in the compounds. However, Zeeman splitting appears in the Mossbauer spectrum of FeNi 2 BO 5 (FeNiBO 4 ) below ca. 102 K (26 K), far above the T N . Further, the Zeeman pattern of FeNi 2 BO 5 shows the presence of spin relaxation in the temperature range of ca. 94 ∼ 107 K, and the quadrupole splitting decreases an order in magnitude and the line width becomes broader compared to the paramagnetic pattern. The origin for these remarkable features are discussed relating to the crystal structures and the magnetic interactions in the compounds.

Piezoelectric ceramics of the PbTiO3-La(Me2/3Nb1/3)O3 (Me: Mg, Zn) solid solution system

Abstract Solid solutions with a perovskite structure are formed in the PbTiO3-La(Me2/3Nb1/3)O3 (Me:Mg,Zn) systems up to about 70 mol% of La(Me2Nb1/3)O3. Structural, dielectric, electromechanical and dilatational properties of the ceramics have been measured as functions of composition and temperature. The electromechanical coupling constants kp and kt at room temperature are 28% and 68%, respectively, in the composition near 10 mol% of La(Mg2/3Nb1/3)O3. The temperature coefficient of the radial mode resonance frequency less than I ppmK−1 is obtained in the vicinity of 10 mol% of La(Me2/3Nb1/3)O3 with a small amount of MnO2 additive.

Annealing effect on magnetic characteristics on (La,Sr)MnO/sub 3/ sputtered films

A perovskite type of (La,Sr)MnO/sub 3/ films were deposited on SiO/sub 2//Si substrates with amorphous surface by using the facing targets sputtering apparatus. Although the film as-deposited at P(O/sub 2/) of 0.3 mTorr was not fully crystallized and the MR ratio was as small as 0.03% at the applied field of 5 kOe, it increased up to 2.5% for the film post-annealed at 850/spl deg/C in air for 10 min. The partial O/sub 2/ pressure P(O/sub 2/) strongly affected their crystallinity as well as the Mn content C/sub Mn/. The film as deposited at P(O/sub 2/) of 0.03 mTorr was composed of crystallites with excellent (100) orientation at relatively low substrate temperature T/sub s/ up to 500/spl deg/C and the large MR ratio of 3.8% was attained even at room-temperature measurement. Since this MR response exhibits excellent linearity, these LSMO films seem to be applied for magnetic sensor devices. It is clarified that the annealing process in preparation of LSMO film effectively increases the MR ratio of the film with insufficient crystallinity, and is not effective for the fully crystallized film.

Dielectric Properties of Ceramics in the Ba(Zn1/3Nb2/3)O3- Sr(Zn1/3Nb2/3)O3 Solid Solutions

Solid solution ceramics in the Ba(Zn1/3Nb2/3)O3-Sr(Zn1/3Nb2/3)O3 system have been studied in view of finding materials for use as dielectric resonators at microwave frequency. The relative dielectric constant of Ba(Zn1/3Nb2/3)O3 and Sr(Zn1/3Nb2/3)O3 ceramics is 41 and 40, and the unloaded Q is 7500 and 4000 at 9 GHz respectively. A nearly zero temperature coefficient of resonant frequency is obtained for a solid solution ceramic with 0.35 BZN-0.65 SZN. The temperature dependence of dielectric constant is discussed in terms of the Clausius-Mossotti relation.

Möossbauer Study of FeMo2S4

Mossbauer spectra of Fe 57 were taken at 79∼300 K for naonoclinic FeMo 2 S 4 with a layered structure. The divalent state of Fe was confirmed and the antiferromagnetic Neel temperature was determined as 101.5±0.5 K. The Fe 2+ spins were shown to lie nearly perpendicular to the a b plane of the monoclinic cell below the Neel point. The paramagnetic spectra taken near the Neel point contained additional unresolved lines, which was considered as a trace of the short range magnetic order due to the two dimensional nature of the magnetic order.

Magnetostriction of SmFeO3 and YFe1-xCox/2Tix/2O3 in the Spin Reorientation Region

Longitudinal and transverse magnetostrictions along the a, b and c axes of SmFeO3 and YFe1-xCox/2Tix/2O3 (0.004x0.012) were measured. In both of the orthoferrites, the magnetostriction increases in magnitude near the spin reorientation temperature region, reaching maximum value of Δl/l~15×10-6 under an external field of 6.8 kOe. The crystals are elongated along the c axis while contracted along the a and b axes when the spontaneous magnetization is rotated from the a toward the c axis by applying the external field, and are distorted in the opposite direction when the magnetization is reversed. It was shown that the magnetostriction of SmFeO3 is roughly proportional to the field induced rotation angle of the magnetization, which is calculated using the empirical magnetic free energy expression. The origin for the magnetostriction is discussed.