Showing papers by "L. E. Cross published in 2002"
TL;DR: The ferroelectric and strain behavior of Ba(Ti1−yCey)O3 solid solutions was studied in this article, where three phase transition temperatures were shifted with increasing Ce concentration, and pinched at y=006.
Abstract: The ferroelectric and strain behavior of the Ba(Ti1−yCey)O3 solid solutions was studied Three phase transition temperatures were shifted with increasing Ce concentration, and pinched at y=006 The samples could be structurally indexed by x-ray diffraction in a tetragonal symmetry at y⩽006; and in a pseudo-cubic symmetry at y>006 The strain levels in the range of 015–019% at ∼60 kV/cm with small hysteresis were obtained for the samples with low content Ce With increasing Ce concentration, the tetragonality decreases, the strain level decreases, and becomes less hysteretic The physical mechanism of the electrostrictive, piezoelectric, and ferroelectric-relaxor behavior is briefly discussed
95 citations
TL;DR: In this paper, the dielectric loss modes of SrTiO3 thin films on different substrates are reported and their physical origin is tentatively attributed to the motion of oxygen vacancies.
Abstract: The dielectric loss modes of SrTiO3 thin films deposited on different substrates are reported. Two dielectric loss modes around 165 and 75 K (at 10 kHz) with field-independent Tm are emphasized. The physical origin of the dielectric modes is discussed and is tentatively attributed to the motion of oxygen vacancies.
40 citations
TL;DR: In this article, the dielectric behavior of the pyrochlore (Bi3/4Zn1/4)2(Zn 1/4Ta 3/4 )2O7 compound has been studied.
Abstract: The dielectric behavior of the pyrochlore (Bi3/4Zn1/4)2(Zn1/4Ta3/4)2O7 compound has been studied. A low-temperature dielectric relaxation was observed in a low-permittivity matrix with e=∼60. The dielectric relaxation process follows a modified Debye model in the vicinity of the relaxation peak, and the relaxation rate follows the Arrhenius law in the wide frequency range 102 to ∼1010 Hz. The temperature intensity of dielectric peaks are independent of dc bias (⩽60 kV/cm). The dielectric relaxation is tentatively attributed to the hopping of Zn/Bi ions at A sites with more than one equivalent potential minima, and the reorientation of the dipoles probably formed through interactions with the “seventh oxygen” and the Bi/Zn A-site ions in the pyrochlore (Bi3/4Zn1/4)2(Zn1/4Ta3/4)2O7 compound.
39 citations
TL;DR: In this paper, the presence of an intermediate ferroelectric orthorhombic phase in oriented 0.92Pb(Zn 1/3 Nb 2/3 )O 3 -0.08PbTiO 3 single crystals was reported.
Abstract: We report the presence of an intermediate ferroelectric orthorhombic FE o phase in oriented 0.92Pb(Zn 1/3 Nb 2/3 )O 3 -0.08PbTiO 3 single crystals. High field-long time poling was done in order to stabilize the inherent symmetry of the crystal. Pyroelectric and dielectric measurements were conducted on d 001 ¢ , d 011 ¢ and d 111 ¢ oriented crystals. Pyroelectric and dielectric peaks corresponding to a ferroelectric rhombohedral FE r to FE o phase transition was observed for d 111 ¢ oriented piezocrystals at ∼80°C.
20 citations
07 Nov 2002
TL;DR: In this article, a 3D-micromachining technique is used to fabricate a MEMS microshell structure that acts as an ultrasound transducer in the 1-5 MHz range.
Abstract: Presents the design, fabrication process and experimental acoustic test data for a novel MEMS-based 2-D ferroelectric ultrasound microshell transducer array. A new 3-D-micromachining technique is used to fabricate a MEMS microshell structure that acts as an ultrasound transducer in the 1-5 MHz range. A rounded sacrificial carbon structure generated by a two-step photo-resist reflow and pyrolysis process provides the shape for the microshell. The variation of process parameters and their affect on the microshell shape are. discussed The piezoelectric monomorph layer is composed of a sol-gel PZT as the active ferroelectric layer deposited on insulating layers of ZrO/sub 2/ and SiN or SiO/sub 2/. A novel in-plane polarization of the PZT is used to maximize sensitivity, while trading off output capacitance to match the CMOS buffer electronics that are required for an arrayed imaging device. Polyimide layers are used to electrically isolate the device from the fluid test environment. Finite element analysis was used to generate expressions describing resonant frequency, volume compliance and receive sensitivity.
13 citations
TL;DR: In this paper, the relaxor ferroelectric copolymers were transformed into a relaxor Ferroelectric phase by high-energy electron irradiation and temperature and frequency dependence of dielectric properties were investigated under dc bias field.
Abstract: Ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymers were transformed into relaxor ferroelectric phase by high-energy electron irradiation. Temperature and frequency dependence of dielectric properties were investigated under dc bias field. The relaxor ferroelectric copolymers show high electrostrictive strain response (Q 12 = 10 m 4 /C 2 ) with an effective d 31 = 180 pm/V at a field of 50 MV/m. Direct piezoelectric response of the relaxor ferroelectric copolymer can be tuned by dc bias, d 31 is measured to be 116 pC/N at 40 MV/m bias field. Electromechanical coupling (k 31 = 0.28 at 60 MV/m bias field) was significantly enhanced in the relaxor ferroelectric copolymers as compared to that in the normal ferroelectric P(VDF-TrFE) copolymers.
8 citations
TL;DR: In this article, the Cole-Cole equation fitting of the frequency dependence of the dielectric constant and loss of Cd 2 Nb 2 O 7 was used to obtain more precise relaxation time data, compared to the data reported in the literature.
Abstract: Dielectric behavior of Cd 2 Nb 2 O 7 has been studied from room temperature down to 10 K with and without dc electric fields. Three dielectric relaxation modes I, II, and III were reexamined. By using the Cole - Cole equation fitting of the frequency dependence of the dielectric constant and loss of Cd 2 Nb 2 O 7 , we have obtained more precise relaxation time data, compared to the data reported in the literature. The results indicate that the relaxation time follows both the Arrhenius law and Vogel - Fulcher relation in the frequency range of 10 2 - 10 5 Hz. With increasing dc bias, the relaxation modes were suppressed and eventually eliminated. The results show a significant suppression of the dielectric constant and loss by the application of dc fields. At above 10 kV/cm, only a dielectric peak remains. The high tunability (37 - 64%) under 15 kV/cm at 5 kHz in the wide temperature range of 50 - 180 K and very low dielectric loss (0.4 - 6 2 10 m 3 )) are observed.
3 citations
TL;DR: In this article, complex dielectric properties of PbZr 1 m x Ti x O 3 ceramics with compositions in the vicinity of the morphotropic phase boundary (x=0.46, 0.48, and 0.51), as a function of dc bias fields, were measured under small ac signal conditions.
Abstract: Complex dielectric properties of PbZr 1 m x Ti x O 3 ceramics with compositions in the vicinity of the morphotropic phase boundary (x=0.46, 0.48, and 0.51), as a function of dc bias fields, were measured under small ac signal conditions. In monoclinic phase, dielectric permittivity shows hysteresis behavior and decreases with increasing bias field when E bias >E c . For compositions of tetragonal phase and near the on-set of the monoclinic phase transitions, dielectric permittivity increases with increasing bias electric field, indicating a continued polarization switching process. Such anomalous behavior is attributed to the E-field induced monoclinic phase, which allows polarization rotation without domain reversal. Temperature dependence of the dc biased dielectric property between 12K and 300K is also reported. Dielectric dispersion is mostly clamped out for both PZT 54:46 and PZT 52:48 as temperatures approaching 12K; however, remains significant in PZT 49:51.
2 citations