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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]

In this study, ceramic samples of lead zirconate titanate Pb(Zr0.42Ti0.58)O3 (PZT 42/58) doped with Fe (hard) and Nb (soft) were studied by Raman, infrared (IR) and THz spectroscopy in the temperature range from 900 to 20 K. From the evaluation of the IR and Raman phonons in undoped ceramics, we conclude that tetragonal PZT ceramics undergo a low-temperature phase transition to a tilted phase, revealed by anomalies in phonon parameters and the appearance of new modes. Doped samples also presented similar behaviour. The main differences between undoped and doped ceramics lie in the dielectric behaviour below phonon frequency range, where several mechanisms appear: a soft central mode (CM) located near 1 THz and two relaxations in the GHz range. Both types of doping raise the permittivity values below the phonon frequencies, not only increasing the dielectric contribution of the CM, but also modifying the dielectric response near the GHz range. Soft ceramics show higher permittivity with logarithmic increase at low frequencies, corresponding to an almost frequency-independent value of the dielectric losses below 0.1 GHz. [ABSTRACT FROM AUTHOR]

Novel lead-free piezoelectric single-crystal with a morphotropic boundary composition (0.94Na1/2Bi1/2TiO3-0.06BaTiO3) was characterized by dielectric spectroscopy, far-IR reflectivity and Raman spectroscopy. Analysis of polarized Raman spectra suggests that the three principal Raman bands are associated with polar optic modes. [ABSTRACT FROM AUTHOR]

The recently revealed giant grain size effect on dielectric properties in undoped SrTiO3 ceramics (J. Petzelt et al., J. Phys.: Condens. Matter 19, 196222 (2007) and references therein), was extended to smaller grains of 80 nm mean grain size. Like for previously studied ceramics with larger grain size, in addition to dielectric permittivity also the infrared and Raman responses were studied and discussed. It was shown that the reduced effective permittivity is fully accounted for by the infrared soft mode behaviour and, similar to single crystals and other ceramics studied, no dielectric dispersion appears below the THz frequency range. The rather universal (independent of the grain size and sintering process) double dead layer structure was proposed to be responsible for the observed changes in the infrared and Raman spectra, allowing the grain core to keep the single crystal dielectric function. The outer dead layer shell (obviously charged due to an oxygen deficit) is very thin (∼ 1 nm) having frequency and temperature independent low permittivity (∼ 10) and is responsible for the static permittivity suppression. The inner layer of only slightly distorted perovskite structure is polar with local polarization normal to grain boundaries gradually decreasing towards the grain centre. This polarization and/or the thickness of the polar layers, which compensate the charged grain boundaries, appear to increase on decreasing temperature, particularly below the structural phase transition. Its nature is still not fully understood. In agreement with our previous suggestions, from the Raman data it can be also concluded that in the low-temperature tetragonal phase of all SrTiO3 ceramics, the local tetragonal axes tend perpendicular to the grain boundaries and the tetragonality is strongly reduced compared to single crystals. [ABSTRACT FROM AUTHOR]

Luminescence of Crk3+ centres in Sr1-xCaxTiO3 (x = 0-0.12) reveals an unusual "dielectric related" temperature shift of the R lines, which correlates well with reciprocal dielectric permittivity behaviour and depends on the character of the phase transitions. The position of the R lines shifts to higher energies with Ca addition. Results obtained are attributed to interaction of the impurity centres with the soft TO1 branch, structural changes and random fields, which are inherent in Sr1-xCaxTiO3. [ABSTRACT FROM AUTHOR]

The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼1.54 Å is estimated, which is ∼7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3. [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]

Abstract: Favorable properties of stillwellite-like LaBGeO5 stimulated many attempts to realize them on an industrial scale. However, the growth of stillwellite single crystals is problematic and, because of strong structural anisotropy, dense stillwellite ceramics were not synthesized to date. Unique properties of crystalline LaBGeO5 may be realized via bulk or grain-oriented crystallization of lanthanum borogermanate (LBG) glasses. Nucleation, bulk and surface crystallization including grain-oriented crystallization of LBG glasses are briefly reviewed. Dependence of crystallization behavior of LBG glasses on the synthesis conditions was found to be closely linked with alumina impurities that suppress texture forming but improve glass-forming ability. The latter offers an opportunity to obtain LBG-based glasses of optical quality, containing more than 30mol% rare-earth oxides, for laser and magneto-optical applications. A wide range of active dielectrics in the LBG system covering non-linear optical nano-structures, planar wave guides and textures with excellent pyroelectric activity are expected to be developed. [Copyright &y& Elsevier]

The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼1.54 Å is estimated, which is ∼7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3. [ABSTRACT FROM AUTHOR]

Abstract: In order to inspect bulk properties of the SrTiO3 ceramics grains, dielectric permittivity and temperature shift of a zero-phonon R-emission line of the Cr3+ impurity-ion probes were studied in sol–gel SrTiO3:Cr (3×10−2%) ceramics of the average grain size ∼24μm. We found that non-dispersive permittivity (100Hz to 1MHz) increases on cooling less steeply than in single crystals reaching ∼5000 at 30K. At lower temperatures the dispersion appears and the permittivity saturates at ∼8K (ɛ′≈7000, 400Hz). However, the temperature shift of the R-line in ceramics remains practically identical to that for SrTiO3 single crystals, in which R-line shifts with temperature is Δν ∼1/ɛ′∼ . This indicates that the bulk of the grains in ceramics exhibits properties inherent to SrTiO3 quantum paraelectric, which agrees with the “generalized brick-wall” approach developed recently to describe polarization response of granular high permittivity materials. [Copyright &y& Elsevier]