Infrared dielectric response of the La2/3TiO3–LaAlO3 microwave ceramics system

Crystal structures and structural changes of the compound La 0.68 (Ti 0.95 Al 0.05 )O 3 have been studied using neutron powder diffraction data and the Rietveld method in the temperature range from 251 to 5921C. The Rietveld profile-fitting analyses of the neutron data and the synchrotron diffraction profile revealed that the crystal symmetry of the low-temperature phase of La 0.68 (Ti 0.95 Al 0.05 )O 3 is orthorhombic Cmmm (2a p Â 2a p Â 2a p ; p: pseudo-cubic perovskite). The unit-cell and structural parameters were successfully refined with the orthorhombic Cmmm for the intensity data measured at 251, 1821, and 2861C, and with the tetragonal P4/mmm (a p Â a p Â 2a p ) for intensity data obtained at 3881 and 5921C. The P4/mmm-to-Cmmm phase transition was found to be induced by tilting of the (TiAl)O 6 octahedron. The tilt angle decreased with increasing temperature, reaching 01 at the Cmmm-P4/mmm transition temperature.

Section: Introductionmentioning

confidence: 99%

Neutron Powder Diffraction Study of a Phase Transition in La_0.68(Ti_0.95Al_0.05)O₃

Ali¹,

Izumi²,

Yashima³

2006

“…In microwave dielectric ceramics, the loss because of the anharmonicity of the lattice vibration was considered to be an intrinsic loss 4 . This kind of loss can be characterized by using far infrared reflection spectra analysis, 6,9–12 for which the classical oscillator dispersion theory 9,10 or the four parameter damped oscillator model 11,12 was applied. However, the contributions of conductance and relaxation polarization to the microwave dielectric loss have not been clearly comprehended.…”

Section: Introductionmentioning

confidence: 99%

Dielectric Loss Spectrum of Ceramic MgTiO₃ Investigated by AC Impedance and Microwave Resonator Measurements

Kuang

Jing

Tang

2005

MgTiO3 ceramic was selected as a model material of the microwave dielectric ceramics for the investigation of the dielectric loss spectrum. Conductivity spectra in the low‐frequency range 1–106 Hz at elevated temperatures and the dielectric loss spectrum in the microwave range 6–14 GHz at room temperature were characterized by AC impedance spectroscopy and the microwave resonator method, respectively. The experimental data were analyzed by using Jonscher's universal power law, the Arrhenius equation as well as the classic dispersion theory. Consequently, a dielectric loss spectrum (tg δ∼f plot) at room temperature in a wide frequency range was obtained. Based on the loss spectrum, the dielectric loss can be classified into three mechanisms in MgTiO3 ceramic (each dominates the loss in different frequency ranges): DC conductance (in DC field), AC conductance (<107 Hz), and anharmonicity of lattice vibration (in GHz range). The influence of defects on the microwave dielectric loss possibly is because of atom defects via damage of the perfection of lattice and modification of the anharmonic force in lattice, while the electronic defects trapped on the atomic defects affect the DC and AC losses.

“…[1][2][3] Therefore, several researchers have investigated the phase relationship, 4 the lattice parameters, and the structural parameters 1,2,5-8 of the compounds. These compounds have a perovskite-related structure with an ordered arrangement of A-site vacancies along the c-axis (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…T HE A-site deficient La (2ϩx)/3 (Ti 1Ϫx Al x )O 3 perovskite compounds are attractive materials because of their electrical and dielectric properties. [1][2][3] Therefore, several researchers have investigated the phase relationship, 4 the lattice parameters, and the structural parameters 1,2,5-8 of the compounds. These compounds have a perovskite-related structure with an ordered arrangement of A-site vacancies along the c-axis (Fig.…”

Section: Introductionmentioning

confidence: 99%

Crystal Structure Refinement of La_0.683(Ti_0.95Al_0.05)O₃ Perovskite by the Rietveld Method

Ali

Yashima

Yoshimura

et al. 2001

The structural parameters of orthorhombic and tetragonal phases (space group P/mmm and P4/mmm) of A-site deficient La 0.683 (Ti 0.95 Al 0.05 )O 3 perovskite have been refined by Rietveld analysis through the X-ray powder diffraction patterns measured in the temperature range from 15°to 500°C. With an increase in temperature the unit-cell parameters a, b, and c increased, while the b/a ratio decreased and became unity between 200°and 400°C. No significant changes were observed for atomic coordinates throughout the temperature studied. These results strongly suggest that the phase transition is induced by lattice distortion.