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A5B4O15 microwave ceramics were investigated to determine their high frequency dielectric characteristics.

The dielectric behavior of (Pb1-x/2Lax)(Zr0.9Ti0.1)O3 PLZT 100x/90/10 (0≤100x≤1) was studied in the frequency range 102-1014 Hz using dielectric, time-domain terahertz (THz), far-infrared, and Raman spectroscopy in the temperature interval 10-900 K. PZT 90/10 and PLZT 2/90/10 undergo two phase transitions, from a cubic paraelectric to a rhombohedral untilted ferroelectric (FE) phase and on further cooling to a tilted FE phase. PLZT 4/90/10 and PLZT 10/90/10 are incommensurately modulated and composed of an intergrowth of polar and antipolar cation displacements. These samples consequently demonstrate a FE soft mode which exhibits minimal frequency several tens of degrees above the nominal antiferroelectric phase transition temperature. The dielectric response of PLZT 100x/90/10 is mainly governed by a gigahertz relaxation and a soft phonon component in the THz range. As in other PbO-based perovskites, the soft mode is split into a higher-frequency component (ω∼80 cm-1) and a highly damped THz component (ω∼30 cm-1), with larger dielectric strength already in the paraelectric phase. [ABSTRACT FROM AUTHOR]

The dielectric behavior of (Pb1-x/2Lax)(Zr0.9Ti0.1)O3 PLZT 100x/90/10 (0≤100x≤1) was studied in the frequency range 102-1014 Hz using dielectric, time-domain terahertz (THz), far-infrared, and Raman spectroscopy in the temperature interval 10-900 K. PZT 90/10 and PLZT 2/90/10 undergo two phase transitions, from a cubic paraelectric to a rhombohedral untilted ferroelectric (FE) phase and on further cooling to a tilted FE phase. PLZT 4/90/10 and PLZT 10/90/10 are incommensurately modulated and composed of an intergrowth of polar and antipolar cation displacements. These samples consequently demonstrate a FE soft mode which exhibits minimal frequency several tens of degrees above the nominal antiferroelectric phase transition temperature. The dielectric response of PLZT 100x/90/10 is mainly governed by a gigahertz relaxation and a soft phonon component in the THz range. As in other PbO-based perovskites, the soft mode is split into a higher-frequency component (ω∼80 cm-1) and a highly damped THz component (ω∼30 cm-1), with larger dielectric strength already in the paraelectric phase. [ABSTRACT FROM AUTHOR]

We prepared multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22 ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at TC=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal. Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near TC. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D3d5 hexagonal structure. No evidence for a structural phase transition was found in the IR and Raman spectra on cooling (in zero magnetic field) or in the room-temperature IR spectra with external static magnetic field up to 0.3 T. [ABSTRACT FROM AUTHOR]

Dielectric spectra of two K0.5Na0.5NbO3 ceramics with different grain sizes (10 and 0.5 μm) were measured from 102 to 1014 Hz in a broad temperature range. The sequence of first-order phase transitions (cubic-tetragonal-orthorhombic-rhombohedral) was detected by differential scanning calorimetry, dielectric spectroscopy, and time-domain terahertz spectroscopy. The grain size affects all the phase transitions, which are more smeared in the small-grain sample. In the large-grain ceramics, two well-separated near-Debye relaxations are seen in the tetragonal phase, which suddenly merge on cooling across the tetragonal-orthorhombic transition, and on further cooling the lower-frequency relaxation strongly broadens. On reducing the grain size, the higher-frequency relaxation shifts from ∼1 to ∼20 GHz and the lower-frequency one strongly broadens. Without quantitative understanding, these effects could be assigned to domain-wall dynamics and its temperature and grain-size dependences. Similar to pure KNbO3, an overlapped central-mode–soft-mode type excitation was detected in the terahertz range related to the effective hopping and oscillations of the off-centered Nb ions in a multiwell potential. [ABSTRACT FROM AUTHOR]

The dielectric behavior of tetragonal (Pb1-xLax)(Zr0.4Ti0.6)O3 (PLZT x/40/60) ceramics doped with lanthanum (x=12% and 15%) has been investigated from 102 to 1014 Hz in the temperature range of 20–800 K. Relaxor ferroelectric behavior, together with a first-order ferroelectric phase transition at TC below the dielectric maximum, was revealed. The lowest-frequency phonon partially softens to TC and splits into two components in the ferroelectric phase. It is shown that similar splitting is typical for all relaxors even for samples without ferroelectric phase transitions, because the TO1 splitting occurs due to a local distortion in the polar clusters. A relaxational mode, assigned to the dynamics of polar clusters, was revealed in the teraherz spectra below 800 K. This mode slows down to the microwave range on cooling and finally anomalously broadens below TC, which appears to be characteristic for all relaxors. In comparison to the rhombohedral (Pb1-xLa0.095)(Zr0.65Ti0.35)O3, the low-temperature permittivity and dielectric losses are lower in the tetragonal PLZT as expected from the presence of the ferroelectric phase transition. [ABSTRACT FROM AUTHOR]

The dielectric behavior of tetragonal (Pb1-xLax)(Zr0.4Ti0.6)O3 (PLZT x/40/60) ceramics doped with lanthanum (x=12% and 15%) has been investigated from 102 to 1014 Hz in the temperature range of 20–800 K. Relaxor ferroelectric behavior, together with a first-order ferroelectric phase transition at TC below the dielectric maximum, was revealed. The lowest-frequency phonon partially softens to TC and splits into two components in the ferroelectric phase. It is shown that similar splitting is typical for all relaxors even for samples without ferroelectric phase transitions, because the TO1 splitting occurs due to a local distortion in the polar clusters. A relaxational mode, assigned to the dynamics of polar clusters, was revealed in the teraherz spectra below 800 K. This mode slows down to the microwave range on cooling and finally anomalously broadens below TC, which appears to be characteristic for all relaxors. In comparison to the rhombohedral (Pb1-xLa0.095)(Zr0.65Ti0.35)O3, the low-temperature permittivity and dielectric losses are lower in the tetragonal PLZT as expected from the presence of the ferroelectric phase transition. [ABSTRACT FROM AUTHOR]

Far-infrared reflectivity spectra of [ Pb(Zn[sup 1/3]Nb[sub 2/3])O[sub 3]][sub 0.92]-[PbTiO[sub 3][sub 0.08] and [Pb(Mg[sub l/3]Nb[sub 2/3])O[sub 3]][sub 0.71]-[PbTiO[sub 3]][sub 0.29] single crystals were investigated between 10 and 530 K, micro-Raman spectra were recorded between 300 and 800 K. No phonon softening was observed near either of the ferroelectric phase transitions. The low-frequency dielectric anomaly in the paraelectric phase is caused by contribution of dynamic polar nanoclusters with the main dispersion in the microwave range. Infrared and Raman spectra confirm the locally doubled unit cell (Z[sub prim] = 2) in the paraelectric and ferroelectric phases due to the ordering in the perovskite B sites and occurrence of polar nanoclusters in the paraelectric phase. The lowest-frequency transverse optical (TO[sub 1]) phonon mode active in the infrared spectra is underdamped in contrast to the recent result of inelastic neutron scattering, where no TO[sub 1] mode could be observed for the wave vectors q ≤ 0.2 Å[sup -1]. This discrepancy was explained by different q vectors probed in infrared and neutron experiments. The infrared probe couples with very long-wavelength phonons (q≈10[sup -5] Å[sup -1]) which see the homogeneous medium averaged over the nanoclusters, whereas the neutron probe couples with phonons whose wavelength is comparable to the nanocluster size (q≥10[sup -2] Å[sup -1]). [ABSTRACT FROM AUTHOR]

A combination of Raman spectroscopy and several other techniques is employed to explain the dielectric behavior and other properties exhibited by the ([Pb.sub.1-x/2][La.sub.x])([Zr.sub.0.9][Ti.sub.0.1])[O.sub.3] compounds. The occurrence of a gigahertz relaxation and soft phonon component in the system is shown to be the main mechanisms behind the studied behavior.

Multiferroic Y-type hexaferrite [Ba.sub.0.5][Sr.sub.1.5][Zn.sub.2][Fe.sub.12][O.sub.22] ceramics are prepared and their magnetic and dielectric properties are compared with single crystal. Ferroelectric (FE) phase is induced by external magnetic field in all samples and the phase diagram in ceramics has resembled that of the single crystal.

Differential scanning calorimetry, dielectric spectroscopy, and time-domain terahertz spectroscopy are used to detect the sequence of first-order phase transitions for dielectric spectra of two [K.sub.0.5][Na.sub.0.5]Nb[O.sub.3] ceramics with different grain sizes. An overlapped central-mode-soft-mode type excitation detected in the terahertz range related to the effective hopping and oscillations of the off-centered Nb ions in a multiwell potential is similar to those observed in the pure KNb[O.sub.3].

The lattice dynamics in all three crystal phases namely cubic, tetragonal and rhombohedral of [Pb(Mg(sub 1/3)Nb(sub 2/3))O3]-[PbTiO3] (PMN-PT) and [Pb(Zn(sub 1/3)Nb(sub 2/3))]O3]-[PbTiO3] (PZN-PT) single crystals are studied by means of infrared (IR) and Raman spectroscopies. IR and Raman spectroscopy confirm the locally doubled unit cell in the paraelectric and ferroelectric phases due to the ordering in the perovskite B sites and occurrence of polar nanoclusters in the paraelectric phase.

The Raman modes of α-quartz-type boron phosphate were found to be extremely stable in frequency over a large temperature range from 300–1000 K. In order to determine the origin of this behavior, the material was also studied at high pressure up to 6 GPa. Upon compression, a classical behavior was observed with mode Grüneisen parameters ranging from −0.08(2) to 3.0(1). The present results indicate that the high temperature behavior in this material is an example of an unusual compensation effect between phonon–phonon interactions and implicit contributions due to thermal expansion. Phonon stability is of utmost importance for materials properties that are dependent on it such as dielectric and piezoelectric properties, for example. Boron phosphate belongs to the important class of α-quartz-type piezoelectric materials for which temperature stability is of primordial importance for resonator and sensor applications. [ABSTRACT FROM AUTHOR]

In an attempt to contribute to understanding of structure-property relationship in ferroelectric relaxor SrBaNbO, we studied X-ray diffuse scattering for compositions with x = 0.35 and x = 0.81 at room temperature. Within signal-rich reciprocal-space images, features related to (i) local deformation due to chemical inhomogeneity, (ii) incommensurate modulation and (iii) fluctuation of polarization have been identified. There are substantial differences between the two compositions, some of which can be straightforwardly attributed to different states of ferroelectric ordering in these materials. In the Sr-rich composition, we have observed additional features in the form of -oriented streaks on planes. They indicate that transverse correlation of uniaxial polarization is anisotropic. At the same time, the fact that streaks appear also on the superlattice planes raises the question whether the modulation and polarization order parameter are interrelated. [ABSTRACT FROM AUTHOR]

A systematic study of the Raman spectra of Pb(Zr1-xTix)O3 (PZT) ceramics has been performed in a broad temperature interval (10-600 K) and a broad Ti/Zr concentration range around the morphotropic phase boundary (x = 0.25-0.70). The number of the spectral components was estimated by a standard fitting procedure with damped harmonic oscillators as well as by counting the number of peaks and shoulders with the help of a purposely designed mathematical analysis based on frequency derivatives of the Raman spectra. This last method proves to be very useful to study Raman spectra of disordered materials. For the case of PZT, the comparison with the Raman modes of PbTiO3 allows us to assign the phonon bands on both sides of the morphotropic phase boundary, and the crossover from the tetragonal to rhombohedral phase spectra is clearly visible. However, there are no indications of a systematic splitting of the JS-symmetry modes into monoclinic A'-A" doublets in the morphotropic samples. Detailed adjusting of the response function to the spectrum requires to assume additional Raman-active modes, but this holds for a much broader concentration range than that of the anticipated monoclinic phase. In particular, the lowest frequency transverse optic mode of E-symmetry (soft mode of the ferroelectric phase transition) is split into two components, a THz frequency anharmonic (central modelike) component and a resonant component (at ω ~ 80 cm-1), both related to the same normal coordinate. The additional Raman band appearing in this frequency range (ω ~ 65 cm-1) at low temperatures is rather associated with the antiphase tilt vibrations of the oxygen octahedra. [ABSTRACT FROM AUTHOR]