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Microwave (MW) transmission, absorption, and reflection loss spectra of the ferrimagnetic U-type hexaferrite Sr4CoZnFe36O60 ceramics were studied from 100 MHz to 35 GHz at temperatures between 10 and 390 K. Nine MW magnetic excitations with anomalous behavior near ferrimagnetic phase transitions were revealed. They also change under the application of the weak bias magnetic field (0–700 Oe) at room temperature. Six pure magnetic modes are assigned to dynamics of the magnetic domain walls and inhomogeneous magnetic structure of the ceramics, to the natural ferromagnetic resonance (FMR), and to the higher-frequency magnons. Three modes are considered the magnetodielectric ones with the dominating influence of the magnetic properties on their temperature and field dependences. The presence of the natural FMR in all ferrimagnetic phases proves the existence of the non-zero internal magnetization and magnetocrystalline anisotropy. Splitting of the FMR into two components without magnetic bias was observed in the collinear phase and is attributed to a change in the magnetocrystalline anisotropy during phase transition. The high-frequency FMR component critically slows down to phase transition. At room temperature, FMR splitting and essential suppression of the higher-frequency modes were revealed under the weak bias field (300–700 Oe). The highly nonlinear MW response and FMR splitting are caused by the gradual evolution of the polydomain magnetic structure to a monodomain one. The high number of magnetic excitations observed in the MW region confirms the suitability of using hexaferrite Sr4CoZnFe36O60 ceramics as MW absorbers, shielding materials and highly tunable filters. [ABSTRACT FROM AUTHOR]

The crystal structure and dielectric response of lead-free tetragonal tungsten bronze, Sr(sub)2LaTi(sub)2Nb(sub)3O(sub)15 (SLTN) ceramics was studied in a very broad frequency and temperature range. The results show that the ceramics have a relaxor-like behavior that can be generally explained in the framework of polar nanocluster dynamics concept, with some peculiarities in the dielectric response, relaxational and crystal lattice dynamics.

Temperature dependences of the optic phonons in PbSc1/2Ta1/2O3 (PST) sol-gel films deposited on sapphire substrate are studied by means of Fourier transform far-infrared transmission spectroscopy in the temperature range of 20-900 K. In all the four films displaying different B-site order, the transverse-optic (TO) mode near 80 cm(super -1) at 10 K softens on heating to approximately 45 cm(super -1).

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

Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and alternating current (ac) conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness, and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four-contact van der Pauw direct current conductivity measurements and bulk conductivity values extracted from two-contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature. [ABSTRACT FROM AUTHOR]

Recently predicted presence of spin-phonon coupling in the CaMnO3 is experimentally confirmed in infrared (IR), Raman and time-domain THz spectra. Most of phonon frequencies seen below 350 cm-1 exhibit significant shifts on cooling below antiferromagnetic phase transition at TN≅120 K. Moreover, several new modes activate in the IR and Raman spectra on cooling below TN. Sum of phonon contributions to static permittivity exhibits small but reliable anomaly at TN. On the other hand, the spin-phonon coupling is not manifested in temperature dependence of radio-frequency permittivity, because intrinsic permittivity is screened by extrinsic contribution from conductivity, which enhances the permittivity to giant values. [ABSTRACT FROM AUTHOR]

Recently predicted presence of spin-phonon coupling in the CaMnO3 is experimentally confirmed in infrared (IR), Raman and time-domain THz spectra. Most of phonon frequencies seen below 350 cm-1 exhibit significant shifts on cooling below antiferromagnetic phase transition at TN≅120 K. Moreover, several new modes activate in the IR and Raman spectra on cooling below TN. Sum of phonon contributions to static permittivity exhibits small but reliable anomaly at TN. On the other hand, the spin-phonon coupling is not manifested in temperature dependence of radio-frequency permittivity, because intrinsic permittivity is screened by extrinsic contribution from conductivity, which enhances the permittivity to giant values. [ABSTRACT FROM AUTHOR]

Complex dielectric properties of PbFe1/2Nb1/2)O3 ceramics were investigated in a broad frequency range from 100 Hz up to 90 THz. A broad dielectric anomaly was observed near the temperature of the ferroelectric phase transition (TC1=376 K). Below 1MHz, the anomaly is strongly influenced by conductivity of the sample, but higher frequency data taken up to 81 MHz reveal a broad and frequency independent peak at TC1 typical for a diffuse ferroelectric phase transition. Surprisingly, dielectric permittivity measured at 37 GHz exhibits a peak shifted by 25K above TC1, which indicates polar nanoregions with dynamics in microwave frequency region. A dielectric relaxation, which appears in THz region below 700 K, slows down towards TC1 and again hardens below TC2=356 K. This central mode drives both phase transitions, so they belong to order-disorder type, although the polar phonons exhibit anomalies near both phase transitions. In the paraelectric phase, infrared reflectivity spectra correspond to local Fm3m structure due to short-range chemical ordering of Fe and Nb cations on the B perovskite sites. Moreover, each polar phonon is split due to two different cations on the B sites. Recently, Manley et al. [Nat. Commun. 5, 3683 (2014)] proposed a new mechanism of creation of polar nanoregions in relaxor ferroelectrics. They argued, based on their inelastic neutron scattering studies of PMN-PT, that the TO1 phonon is split and interaction of both components gives rise to so called Anderson phonon localization, which can produce regions of trapped standing waves and these waves induce polar nanoregions in relaxors. We cannot exclude or confirm this mechanism, but we show that the splitting of polar phonons is a common feature for all complex perovskites with relaxor ferroelectric behavior and it can be also observed in canonical ferroelectric BaTiO3, where the soft mode is split in paraelectric phase due to a strong lattice anharmonicity. [ABSTRACT FROM AUTHOR]

We report measurements of the optical response of polycrystalline DyN thin films. The frequency-dependent complex refractive index in the near IR-visible-near UV was determined by fitting reflection/transmission spectra. In conjunction with resistivity measurements, these identify DyN as a semiconductor with an optical energy gap of 1.2 eV. When doped with nitrogen vacancies it shows free carrier absorption and a blue-shifted gap associated with the Moss-Burstein effect. The refractive index of 2.0 ± 0.1 depends only weakly on energy. Far infrared reflectivity data show a polar phonon of frequency 280 cm-1 and a dielectric strength of Δ[variant_greek_epsilon]=20. [ABSTRACT FROM AUTHOR]

Domain structures of 100-300 nm thin epitaxial films of ferroelectric PbTiO3 grown by metalorganic chemical vapor deposition technique on LaAlO3 perovskite substrate have been investigated by piezoresponse force microscopy and infrared reflectance spectroscopy techniques. Normal-incidence reflectance spectra reveal both E- and A1-symmetry modes of PbTiO3. The latter ones demonstrate the presence of a minor fraction of a-domains (with in-plane orientation of the spontaneous polarization) in the film. The piezoresponse force microscopy images allow to get local insight in the complex nanodomain architecture composed by few hundred nm large areas of primarily c/a/c/a but also a1/a2/a1/a2 domain pattern types, with participation of all six tetragonal ferroelectric domain states and both 180 ° and 90 ° ferroelectric walls. [ABSTRACT FROM AUTHOR]

High-frequency dielectric studies of Bi0.85Nd0.15FeO3 ceramics performed betweeen 100 and 900 K reveal hardening of most polar phonons on cooling below antiferroelectric phase transition, which occurs near 600 K. Moreover, a strong THz dielectric relaxation is seen in paraelectric phase. Its relaxation frequency softens on cooling towards TC ≈ 600 K, its dielectric strength simultaneously decreases, and finally the relaxation disappears from the spectra below 450 K. Both phonon and dielectric relaxation behavior are responsible for a decrease in the dielectric permittivity at the antiferroelectric phase transition. Origin of unusual strong THz dielectric relaxation in paraelectric phase is discussed. Bi0.85Nd0.15FeO3 structure lies on the phase boundary between polar rhombohedral and non-polar orthorhombic phase and owing to this, the polarization rotation and polarization extension can enhance the piezoelectric response of this system. Similarities and discrepancies with lead-based piezoelectric perovskites, exhibiting morphotrophic phase boundary between two ferroelectric phases, are discussed. [ABSTRACT FROM AUTHOR]

A thin dielectric resonator consisting of a dielectric substrate and the thin film deposited upon it is shown to suffice for microwave characterization and dielectric parameter measurement of high-permittivity thin films without electrodes. The TE01δ resonance mode was excited and measured in thin (down to 0.1 mm) rectangular- or disk-shaped low-loss dielectric substrates (D∼10 mm) with permittivity [variant_greek_epsilon]′≥10 inserted into a cylindrical shielding cavity or rectangular waveguide. The in-plane dielectric permittivity and losses of alumina, DyScO3, SmScO3, and (LaAlO3)0.29(SrAl1/2Ta1/2O3)0.71 (LSAT) substrates were measured from 10 to 18 GHz. The substrate thickness optimal for characterization of the overlying thin film was determined as a function of the substrate permittivity. The high sensitivity and efficiency of the method, i.e., of a thin dielectric resonator to the dielectric parameters of an overlying film, was demonstrated by characterizing ultrathin strained EuTiO3 films. A 22 nm thick EuTiO3 film grown on a (100) LSAT substrate and strained in biaxial compression by 0.9% exhibited an increase in microwave permittivity at low temperatures consistent with it being an incipient ferroelectric; no strain-induced ferroelectric phase transition was seen. In contrast, a 100 nm thick EuTiO3 film grown on a (110) DyScO3 substrate and strained in biaxial tension by 1% showed two peaks as a function of temperature in microwave permittivity and loss. These peaks correspond to a strain-induced ferroelectric phase transition near 250 K and to domain wall motion. [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]

Sr2TiMnO6, a double perovskite associated with high degree of B-site cation disorder was investigated in detail for its structural, magnetic, and dielectric properties. Though x-ray powder diffraction analysis confirms its cubic structure, first order Raman scattering and infrared reflectivity spectra indicate a breaking of the local cubic symmetry. The magnetization study reveals an anomaly at 14 K owing to a ferrimagnetic/canted antiferromagneticlike ordering arising from local Mn-O-Mn clusters. Saturated M-H hysteresis loops obtained at 5 K also reflect the weak ferromagnetic exchange interactions present in the system and an approximate estimation of Mn3+/Mn4+ was done using the magnetization data for the samples sintered at different temperatures. The conductivity and dielectric behavior of this system has been investigated in a broad temperature range of 10 to 300 K. Intrinsic permittivity was obtained only below 100 K whereas giant permittivity due to conductivity and Maxwell-Wagner polarization was observed at higher temperatures. X-ray photoemission studies further confirmed the presence of mixed oxidation states of Mn and the valence band spectra analysis was carried out in detail. [ABSTRACT FROM AUTHOR]

We investigate 100 nm thick epitaxial monolayer of SrTiO3 strained by 1% in biaxial tension and grown on (110) DyScO3. Spectra within the whole far-infrared spectral range are obtained as a function of temperature and an electric bias. An appreciable tunability of high frequency polar phonons is observed upon bias. The splitting of TO4 mode clearly observed below 220 K, which is further increased upon bias, is a signature of the ferroelectricity of the film at these temperatures. [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]

The paper describes experiments revealing the anisotropy of the macroscopic dielectric response of poled lead zirconate titanate ceramics in the phonon frequency region. The results are discussed in terms of distinct polar phonon contributions and effective medium theory. The anisotropy probed in far-infrared experiments can be used to evaluate efficiency of the poling and/or depoling processes. [ABSTRACT FROM AUTHOR]

We investigated the ceramics samples of multiferoic solid solution of relaxor ferroelectric Pb(Fe2/3W1/3)O3 with ferroelectric PbTiO3 (abbreviated as PFW-xPT; x=0, 0.25, and 0.37) by means of acoustic emission (AE) method and simultaneously using the dielectric measurement below 700 K. A distinct AE response has been detected at Burns temperature Td≈640–650 K, where the dynamic polar clusters start to appear, at intermediate temperature of 510–520 K, where the polar clusters become probably static, at ferroelectric phase transition temperatures Tc, and at Néel antiferromagnetic phase transitions. The Néel temperatures TN in ceramics were observed to be lower than in the crystals; the origin is discussed. Based on detected AE responses, we have corrected previously obtained phase diagram for PFW-xPT system. [ABSTRACT FROM AUTHOR]

Relaxor ferroelectric PbMg1/3Ta2/3O3 ceramics and thin films were investigated by means of broad-band dielectric, time-domain terahertz (THz), and Fourier-transform infrared (IR) spectroscopy in the frequency range 100 Hz–90 THz at temperatures 100–490 K; the THz and IR spectra were studied from 20 to 900 K. A diffused and strongly temperature dependent peak in the complex permittivity is caused by a dielectric relaxation due to the dynamics of polar clusters. The relaxation appears below the Burns temperature Td in the THz range; it slows down on cooling through the microwave and MHz range and anomalously broadens. The shortest and longest relaxation times of the distribution of relaxation times follow Arrhenius and Vogel–Fulcher laws, respectively. The degree of the B-site order has only a small influence on the parameters of the dielectric relaxation and almost no influence on the phonon parameters. Below Tm≅180 K the distribution of relaxation frequencies becomes broader than our experimental spectral range, and frequency independent dielectric losses develop below 100 GHz in the spectra. Although the macroscopic crystal structure is cubic, IR spectra give evidence about the lower local symmetry, which can be assigned to the presence of the polar clusters below Td. Infrared spectra above Td still reveal more modes than predicted by selection rules in the paraelectric phase of the Fm3m space group so that we suggest selection rules which take into account chemical inhomogeneity in the β″-perovskite sublattice. [ABSTRACT FROM AUTHOR]

Relaxor ferroelectric PbMg1/3Ta2/3O3 ceramics and thin films were investigated by means of broad-band dielectric, time-domain terahertz (THz), and Fourier-transform infrared (IR) spectroscopy in the frequency range 100 Hz–90 THz at temperatures 100–490 K; the THz and IR spectra were studied from 20 to 900 K. A diffused and strongly temperature dependent peak in the complex permittivity is caused by a dielectric relaxation due to the dynamics of polar clusters. The relaxation appears below the Burns temperature Td in the THz range; it slows down on cooling through the microwave and MHz range and anomalously broadens. The shortest and longest relaxation times of the distribution of relaxation times follow Arrhenius and Vogel–Fulcher laws, respectively. The degree of the B-site order has only a small influence on the parameters of the dielectric relaxation and almost no influence on the phonon parameters. Below Tm≅180 K the distribution of relaxation frequencies becomes broader than our experimental spectral range, and frequency independent dielectric losses develop below 100 GHz in the spectra. Although the macroscopic crystal structure is cubic, IR spectra give evidence about the lower local symmetry, which can be assigned to the presence of the polar clusters below Td. Infrared spectra above Td still reveal more modes than predicted by selection rules in the paraelectric phase of the Fm3m space group so that we suggest selection rules which take into account chemical inhomogeneity in the β″-perovskite sublattice. [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]

Lead-free tetragonal tungsten bronze Sr2LaTi2Nb3O15 ceramics were prepared and its crystal structure determined. Dielectric response of Sr2LaTi2Nb3O15 was investigated in a broad frequency (100 Hz–90 THz) and temperature range. The observed relaxor-like behavior can be generally described in the framework of polar nanocluster dynamics concept. However, some peculiarities in the dielectric response, relaxational, and crystal lattice dynamics (e.g., hardly resolved Vogel–Fulcher part of the relaxation, reduced dielectric strength of the cluster flipping mechanism, absence of ferroelectric phase under electric field, absence of the polar soft phonon, etc.) were revealed. Therefore, we claim that Sr2LaTi2Nb3O15 is more alike to dipolar glasses than lead-based perovskite relaxor ferroelectrics. [ABSTRACT FROM AUTHOR]

Temperature dependences of the optic phonons in PbSc1/2Ta1/2O3 (PST) sol-gel films deposited on sapphire substrates were studied by means of Fourier transform far-infrared transmission spectroscopy in the temperature range of 20–900 K. Four films displaying different B-site order with both ferroelectric and relaxor behavior were studied. In all cases the TO mode near 80 cm-1 at 10 K softens on heating to ≈45 cm-1 following the Cochran law with extrapolated critical temperature near 700 K which is 400 K above the temperature of dielectric maximum, Tm. Above 600 K the TO1 mode remains stabile. This mode can be assigned to the A1 component of the ferroelectric soft-mode inside polar clusters which form below the Burns temperature near 700 K. In the ordered PST film another mode activates below Tm in the infrared spectra near 60 cm-1, also exhibiting an anomalous temperature dependence due to its coupling with the former mode. It is assigned to the A1 component of the F2g Raman active mode. The central mode, which appears below the Burns temperature in the terahertz range, is assigned to the dynamics of polar clusters. It slows down on cooling and vanishes from our spectral range below Tm. Another overdamped excitation assigned to the E component of the soft mode appears near 30 cm-1 at low temperature. [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.

The x-ray power diffraction analysis approach is employed to explain the structural, magnetic, as well as the dielectric properties of the [Sr.sub.2]TiMn[O.sub.6] ceramics. The ceramics are shown to exhibit saturated M-H hysteresis loops at 5 K, which are shown to demonstrate numerous weak ferromagnetic exchange interactions among them.

Epitaxial monolayer of SrTi[O.sub.3] strained by 1% in biaxial tension and grown on (110) DySc[O.sub.3] is examined. Spectra within the whole far-infrared spectral range are achieve as a function of temperature and electric bias and an appreciable tenability of high frequency polar phonons is seen upon bias.

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.

The ceramics samples of multiferoic solid solution of relaxor ferroelectric Pb([Fe.sub.2/3][W.sub.1/3])[O.sub.3] with ferroelectric PbTi[O.sub.3] are examined by using acoustic emission (AE) method and the dielectric measurement below 700 K. The Neel temperatures [T.sub.N] in ceramics are lower than in the crystals.

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.

High-frequency dielectric properties of A[sub 5]B[sub 4]O[sub 15] (A=Ba, Sr, Mg, Zn, Ca; B=Nb, Ta) dielectric ceramics are studied by means of the microwave cavity technique, a combination of far-infrared reflection and transmission spectroscopy and time-resolved terahertz transmission spectroscopy. Microwave permittivity ε′ and Qxf factor vary, depending on the chemical composition, between 11 and 51, and 2.4 and 88 THz, respectively. The temperature coefficient τ[sub f] varies between -73 and 232 ppm/°C, and in two samples |τ[sub f]| is less than 15 ppm/°C. It is shown that the microwave permittivity ε′ of the ceramics studied is determined by the polar phonon contributions and that linear extrapolation of the submillimeter dielectric loss ε″ down to the microwave region is in agreement with the microwave data of single phase samples. The relationship among phonon spectra, the crystal structure, and the unit cell volume is discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and alternating current (ac) conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness, and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four-contact van der Pauw direct current conductivity measurements and bulk conductivity values extracted from two-contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature. [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]

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]