Search

Magnetic resonance spectra of EuTiO

We report an investigation of hexagonal Y_(1-x)Eu_xMnO_3 ceramics with x=0, 0.1 and 0.2 using infrared and THz spectroscopies in the temperature range between 5 and 900 K. The temperature dependence of the THz permittivity reveals a kink near the antiferromagnetic phase transition temperature T_N ~ 70 K giving evidence of a strong spin-lattice coupling. Below T_N two absorption peaks were revealed in the THz spectra close to 43 and 73 cm-1. While the first peak corresponds to a sharp antiferromagnetic resonance exhibiting softening on heating towards TN, the second one may be attributed to an impurity mode or a multiphonon absorption peak. High-temperature THz spectra measured up to 900 K reveal only small gradual increase of the permittivity in agreement with a weak phonon softening observed in the infrared reflectance spectra upon heating. This corresponds to an improper ferroelectric character of the phase transition proposed from first principle calculations by Fennie and Rabe [Phys. Rev. B 72 (2005), pp. 100103(R)]., Comment: Phase Transitions, accepted

We describe the first-principles design and subsequent synthesis of a new material with the specific functionalities required for a solid-state-based search for the permanent electric dipole moment of the electron. We show computationally that perovskite-structure europium barium titanate should exhibit the required large and pressure-dependent ferroelectric polarization, local magnetic moments, and absence of magnetic ordering even at liquid helium temperature. Subsequent synthesis and characterization of Eu$_{0.5}$Ba$_{0.5}$TiO$_3$ ceramics confirm the predicted desirable properties.

Infrared reflectivity spectra of antiferromagnetic incipient ferroelectric EuTiO3 were investigated up to 600 K. Three polar phonons typical for the cubic perovskite $Pm\bar {3}m$ structure were observed. Analysis of phonon plasma frequencies showed that the lowest-energy TO1 phonon corresponds predominantly to the Slater mode describing vibration of Ti cations against the oxygen octahedra and the TO2 phonon expresses vibrations of the Eu cation against the TiO6 octahedra. The highest frequency TO4 phonon represents O-octahedra bending. Incipient ferroelectric behavior of the permittivity is caused by pronounced softening of the TO1 phonon, which is coupled to the TO2 mode. Although the Eu cations are not involved in the TO1 mode, the spin ordering of the 4f electrons at Eu cations has influence on the frequency of the TO1 mode due to Eu-O-Eu super-exchange interaction. This is probably responsible for the 7% change of the permittivity induced by the magnetic field in the antiferromagnetic phase, as reported by Katsufuji and Takagi [Phys. Rev. B 64, 054415 (2001)].

We investigated the grain size effect on the high temperature behaviour of PMN-35PT ceramics around the tetragonal–cubic phase transition using second harmonic generation (SHG) and dielectric spectroscopy. Our data revealed coexistence of the first-order ferroelectric phase transition and relaxor behaviour in the coarse grain (grain size ∼4 µm) µ_PMN-35PT. The phase transition is hindered and relaxor features prevail in the fine grain (grain size ∼150 nm) n_PMN-35PT ceramics. Effect of the grain-size reduction on the SHG and dielectric response could be attributed to stabilisation of intermediate domain configurations between the frozen polar nanoclusters and large ferroelectric domains and to the enhanced stability of polar nanoclusters in the fine grain ceramics.

Temperature dependence of the optic phonons in 0.4PbMg 1/3 Nb 2/3 O 3 –0.3PbSc 1/2 Nb 1/2 O 3 –0.3PbZn 1/3 Nb 2/3 O 3 (0.4PMN–0.3PSN–0.3PZN) ceramics were studied by means of FTIR reflection and THz transmission spectroscopy in the temperature range of −253.15 to 226.85 °C. On heating from low temperatures, the A 1 component of the strongly split TO 1 mode softens towards the Burns temperature, but the softening ceases near 126.85 °C which could be a signature of polar cluster percolation temperature. Surprisingly, the TO 2 mode also softens on heating and follows the Cochran law with extrapolated critical temperature close to the melting point.

Dielectric inhomogeneities may have rather pronounced effect on the measured effective permittivity and dielectric function in high-permittivity dielectrics including the polar phonon response. We address the effect of grain boundaries in SrTiO3 and BaTiO3 ceramics and nanograin ceramics and estimate the dead-layer properties in the grain-boundary region using the generalized brick-wall model. Also we discuss the effective response due to the strong grain anisotropy in the ferroelectric BaTiO3. A new interpretation of the infrared spectra of classical relaxors is suggested, based on the effective medium approach and rather strong polar cluster anisotropy.

The microwave dielectric, Bi 1.5 ZnNb 1.5 O 7 exhibits low-temperature dielectric relaxation. To find the origin of the dielectric relaxation of Bi 1.5 ZnNb 1.5 O 7 , we studied the structure and dielectric behavior of Bi 1.5 ZnNb 1.5 O 7 in detail. The Bi 1.5 ZnNb 1.5 O 7 is not composed of a single phase pyrochlore structure. Instead, it consists of unusual structure of Bi 1.5 Zn 0.92 Nb 1.5 O 6.92 and ZnO. The ZnO is distributed evenly in the grain and at the boundary of the Bi 1.5 Zn 0.92 Nb 1.5 O 6.92 structure. Many small voids (

Microwave dielectric properties of fluorite-like (1 − x )Bi 2 O 3 – x Nb 2 O 5 solid solutions with various x between 0.1 and 0.26 are compared with complex dielectric response in THz and infrared frequency range between 0.1 and 100 THz, which allows the estimation of intrinsic and extrinsic dielectric losses. The best quality sample with the most attractive properties was found for x = 0.26 composition with the permittivity of 86, Qf = 1000 GHz and τ f = 120 ppm/K. Our ceramic system exhibits two different crystal structures depending on Nb 2 O 5 concentration and it is shown how the infrared reflectivity spectra can help to distinguish the structures. τ f can be reduced to zero by mixing of Type II and Type III structures.

Time-domain THz transmission experiment was performed on a $\rm SrBi_2Ta_2O_9$ film deposited on sapphire substrate. Temperatures between 300 and 923 K were investigated and complex permittivity spectra of the film were determined. The lowest frequency optic phonon near 28 cm$^{-1}$ reveals a slow monotonic decrease in frequency on heating with no significant anomaly near the phase transitions. We show that the dielectric anomaly near the ferroelectric phase transition can be explained by slowing down of a relaxational mode, observed in the THz spectra. A second harmonic generation signal observed in a single crystal confirms a loss of center of symmetry in the ferroelectric phase and a presence of polar clusters in the intermediate ferroelastic phase., Comment: subm. to J. Phys.: Condens. Matter

Broad-band dielectric spectroscopy including the infrared response of several examples of disordered ferroelectrics is reviewed. The discussed examples belong to dipolar glasses (RADP and DRADP), relaxor ferroelectrics (PMN, PLZT), relaxor-like ferroelectrics (PZN-PT) and doped incipient ferroelectrics (KLT, KTN, SBiT). Common features to all the examples are summarised and differences among the mentioned classes of materials are pointed out.

Low-frequency (100 Hz-1 MHz) dielectric permittivity and infrared reflectivity studies were performed for barium-calcium-titanate single crystals of the congruently melting composition Ba 0.77 Ca 0.23 TiO 3 , nominally pure (BCT77/23) and doped by Cr (70 ppm, BCT77/23:Cr). Both the materials reveal a sharp e'(T) maximum at 375 K (cooling run) with a pronounced temperature hysteresis, evidencing a first-order ferroelectric phase transition (PT) O h → C 4v . The high-temperature wing of the e'(T) maximum reveals a weak dispersion of a non-relaxation nature. The low-temperature wing contains a reproducible step in the e'(T) dependence. Another low-temperature PT was found at ∼41 K. Cr doping strongly influences this PT shifting the position of the e'(T) maximum to ∼20K. Polarised IR reflectivity shows a huge A 1 - E splitting of TO 1 polar phonons below the ferroelectric PT as in the pure BaTiO 3 . IR spectra indicate a displacive and diffuse character for the low temperature PT, but leave open the question about the predominance of displacive or order-disorder character of the high temperature PT.

Far-infrared reflectivity spectra of [Pb(Zn1/3Nb2/3)O3]0.92–[PbTiO3]0.08 and [Pb(Mg1/3Nb2/3)O3]0.71–[PbTiO3]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 (Zprim=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 (TO1) phonon mode active in the infrared spectra is underdamped in contrast to the recent result of inelastic neutron scattering, where no TO1 mode could be observed for the wave vectors q⩽0.2 A−1. This discrepancy was explained by different q vectors probed in infrared ...

Dielectric spectrum of relaxor PLZT exhibits strong broadening on cooling the sample. Below the freezing point constant losses are observed possessing distinct magnitude down to the lowest temperatures. Such behavior is explained considering the thermally activated reversal of the local dipoles (hopping of Pb ions) in dynamical intermediate regions in the frozen phase with the statistically distributed small activated barriers. It is argued that the assumptions of the model are appropriate for perovskite structures in the vicinity of morphotropic boundary.

The aim of this work was to prepare phase pure and dense EuTiO 3 ceramics and to establish their infrared reflectivities. Two kinds of stoichiometric powder mixture (Eu 2 O 3 + Ti 2 O 3 and Eu 2 O 3 + TiO 2 ) were used as precursors for shaping green bodies by cold isostatic pressing. Dense bulk samples were prepared by pressure-less sintering in reducing (Ar + 7%H 2 , 100%H 2 ) conditions in a temperature range of 1300–1650 °C. The sample prepared from Eu 2 O 3 + TiO 2 powder mixture sintered in pure hydrogen at a temperature of 1400 °C for 2 hours exhibited a relative density higher than 95%TD and 100% phase purity, which resulted in its high infrared reflectivity affected by neither low density nor phase impurities.

Infrared reflectivity spectra of cubic SrMnO$_{3}$ ceramics reveal 18 % stiffening of the lowest-frequency phonon below the antiferromagnetic phase transition occurring at T$_{N}$ = 233 K. Such a large temperature change of the polar phonon frequency is extraordinary and we attribute it to an exceptionally strong spin-phonon coupling in this material. This is consistent with our prediction from first principles calculations. Moreover, polar phonons become Raman active below T$_{N}$, although their activation is forbidden by symmetry in $Pm\bar{3}m$ space group. This gives evidence that the cubic $Pm\bar{3}m$ symmetry is locally broken below T$_{N}$ due to a strong magnetoelectric coupling. Multiphonon and multimagnon scattering is also observed in Raman spectra. Microwave and THz permittivity is strongly influenced by hopping electronic conductivity, which is caused by small non-stoichiometry of the sample. Thermoelectric measurements show room-temperature concentration of free carriers $n_{e}=$3.6 10$^{20}$ cm$^{-3}$ and the sample composition Sr$^{2+}$Mn$_{0.98}^{4+}$Mn$_{0.02}^{3+}$O$_{2.99}^{2-}$. The conductivity exhibits very unusual temperature behavior: THz conductivity increases on cooling, while the static conductivity markedly decreases on cooling. We attribute this to different conductivity of the ceramic grains and grain boundaries., Comment: subm. to PRB

The phase purity and the lattice dynamics in bulk EuTiO3 were investigated both microscopically, using X-ray and neutron diffraction, 151-Eu-M\"ossbauer spectroscopy, and 151-Eu nuclear inelastic scattering, and macroscopically using calorimetry, resonant ultrasound spectroscopy, and magnetometry. Furthermore, our investigations were corroborated by ab initio theoretical studies. The perovskite symmetry, Pm-3m, is unstable at the M- and R- points of the Brillouin zone. The lattice instabilities are lifted when the structure relaxes in one of the symmetries: I4/mcm, Imma, R-3c with relative relaxation energy around -25 meV. Intimate phase analysis confirmed phase purity of our ceramics. A prominent peak in the Eu specific density of phonon states at 11.5 meV can be modelled in all candidate symmetries. A stiffening on heating around room temperature is indicative of a phase transition similar to the one observed in SrTiO3, however, although previous studies reported the structural phase transition to tetragonal I4/mcm phase our detailed sample purity analysis and thorough structural studies using complementary techniques did not confirm a direct phase transition. Instead, in the same temperature range, Eu delocalization is observed which might explain the lattice dynamical instabilities.

The success of the ability of the nation itself in increasing the welfare of the people. To improve the well-being of its people, then the necessary funds, one of them through the Earth and building tax. The Earth and building taxes not fully collectible that still lack some of the arrears. To collect the arrears required an exercise of good collection system and organized. Object of the research was conducted at the KPP Pratama Bitung, which retail in this study discusses the evaluation of the implementation of the system of earth and building tax collection at KPP Pratama Bitung. The purpose of the this research is (1) to find out how the implementation of the system of earth and building tax collection at KPP Pratama Bitung, (2) know the level of tax revenues at KPP Pratama Bitung, (3) to find out how well implementation of the Tax collection system at KPP Pratama Bitung. This research uses qualitative data and quantitative data. Analytical method used is descriptive analysis method. The results showed that the implementation of the system of KPP Pratama Bitung in 2009-2011 is already good visible from Earth and building tax receipts that always hit the target set by the Office.

Infrared and Raman spectra of lithium ammonium tartrate monohydrate were obtained in the frequency region at temperatures of 15 - 300 K. No soft phonon mode was observed, so the ferroelastic and ferroelectric phase transition at is of order - disorder type. The ordering of atoms below produces pronounced decreases in the dampings of all phonon modes. The change in the number of infrared and Raman-active modes at the phase transition seems to correspond to the transition from the orthorhombic to a monoclinic phase instead of the recently predicted triclinic low-temperature phase. In contrast to the case for isomorphous lithium thallium tartrate monohydrate, where a substantial increase of with hydrostatic pressure was observed, in the case of LAT crystal decreases only slightly down to 91 K at 400 MPa.

A substantial hardening of the phonon modes near 75 and 90 cm−1 with hydrostatic pressure was observed in the far-infrared spectra of Rochelle salt, but no influence of pressure on the soft mode near 20 cm−1 was found. A large increase in the ferroelectric phase transition temperature with hydrostatic pressure in lithium thallium tartrate monohydrate was seen from dielectric measurements, as well as in the Raman and far-infrared spectra.

The ultrasonic velocity and attenuation of longitudinal waves have been measured along the a, b and c directions as a function of frequency (10 – 70 MHz) and temperature (110 – 300 K) in single - crystal betaine calcium chloride dihydrate. The ultrasonic anomalies were observed at incomplete devil's staircase transition temperatures. The largest anomaly appeared at the normal - incommensurate phase transition at Ti ≈ 164 K Landau theory has been used to explain the experimental data below Ti. From attenuation data, the relaxation time of the amplitudon in the incommensurate phase has been estimated to be τ = (1.3 · 10−13) f 1, where t = (Ti-T)/Ti . In addition, the critical ultrasonic velocity behavior in the hydrodynamic region (ωτ≪ 1) was analyzed in terms of a scaling model. The critical - exponent value was found to be μ ≈ 0.3.

A substantial increase of the ferroelectric phase transition temperature with hydrostatic pressure was observed for lithium thallium tartrate monohydrate single crystals. The temperature dependence of the permittivity shows an unusual shape exhibiting a broad plateau in below . It follows from our hysteresis loop measurements that the domain wall motion freezes approximately 5 - 15 K (this value is pressure dependent) below and causes the drop in . The temperature and pressure dependence of the soft-mode frequency was measured by far-infrared as well as Raman spectroscopy at 10 - 300 K and 0.1 - 440 MPa. The soft mode softens only incompletely because of its strong coupling with a transverse acoustic mode.

Results of our 10 years study of more than 80 microwave ceramics varying in composition and processing with the aid of infrared reflectivity and submillimetre transmission spectroscopy are reviewed. These techniques are unavoidable for understanding the origin of microwave permittivity and losses. Extrapolation from submillimetre to microwave range is discussed as well as the observed steep overall increase in losses on increasing permittivity. The most important structural parameter for dielectric properties is the packing degree. Ideally packed structures show the lowest permittivity and losses. On lowering the packing degree, permittivity and losses increase and the lattice becomes more anharmonic. Extrinsic part of losses due to defects is discussed on the basis of their temperature and frequency dependences, but no clear quantitative conclusions can be drawn in most cases.

We studied the influence of hot-pressing temperature as well as poling and ageing conditions on the amount of polar phase of hot-pressed PVDF and P(VDF/TFE)-(0.98/0.02) foil. FIR transmission spectra of hot-pressed homopolymer and copolymer films were measured in the 30-450 cm -1 range as a function of hot-pressing temperature T hp and poling temperature T p .The FIR studies show that homopolymer and copolymer consist of both polar and nonpolar modifications of PVDF.The content of the polar phase tends to decrease with T hp and increase after poling. The FIR spectra of our samples exhibit a strong absorption peak near 100 cm -1 absent in the biaxially oriented Solef samples, which is believed to be due to the amorphous phase in our samples. Four thermally stimulated current (TSC) maxima are attributed to the relaxation in the amorphous region (∼40 o C), to the dipolar relaxation in the nonpolar (∼60 o C)and polar (∼80 o C) phase, and the space charge relaxation (dependent on the poling temperature). The pyroelectric coefficient of the homopolymerand copolymer thermoelectret foil prepared by hot-pressing is of the same order as that of the PVDF thermoelectret foil produced by Solvay and can be influenced by the hot-pressing conditions. The dielectric response of the hot-pressed PVDF-type foils can be described by the Kohlrausch-Williams-Watts function and is characteristic of a heterogeneous system

We performed factor-group analysis of all phonons in possible monoclinic C2/c and C2 structures of BiMnO3 and compared it with our experimental infrared and Raman spectra. We conclude that the crystal structure is centrosymmetric C2/c in the whole investigated temperature range from 10 to 550 K, therefore BiMnO3 cannot be ferroelectric. We revealed a dielectric relaxation in THz spectra above the structural phase transition taking place at T_C1=475 K giving evidence in strong lattice anharmonicity and a large dynamical disorder of Bi cations above T_C1. Step-like dielectric anomaly observed at T_C1 in THz permittivity reminds antiferroelectric phase transition. Nevertheless, the low-temperature dielectric studies did not reveal any antiferroelectric or ferroelectric hysteresis loop. Our experimental results support theoretical paper of P. Baettig et al. (J. Am. Chem. Soc. 129, 9854 (2007)) claiming that BiMnO3 is not multiferroic, but only antipolar ferromagnet., accepted to JAP

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 Δe=20.

X-ray diffraction, dynamical mechanical analysis and infrared reflectivity studies revealed an antiferrodistortive phase transition in EuTiO3 ceramics. Near 300K the perovskite structure changes from cubic Pm-3m to tetragonal I4/mcm due to antiphase tilting of oxygen octahedra along the c axis (a0a0c- in Glazer notation). The phase transition is analogous to SrTiO3. However, some ceramics as well as single crystals of EuTiO3 show different infrared reflectivity spectra bringing evidence of a different crystal structure. In such samples electron diffraction revealed an incommensurate tetragonal structure with modulation wavevector q ~ 0.38 a*. Extra phonons in samples with modulated structure are activated in the IR spectra due to folding of the Brillouin zone. We propose that defects like Eu3+ and oxygen vacancies strongly influence the temperature of the phase transition to antiferrodistortive phase as well as the tendency to incommensurate modulation in EuTiO3., PRB, in press

Compressively strained epitaxial (001) EuTiO${}_{3}$ thin films of tetragonal symmetry have been deposited on (001) (LaAlO${}_{3}$)${}_{0.29}$-(SrAl${}_{1/2}$Ta${}_{1/2}$O${}_{3}$)${}_{0.71}$ (LSAT) substrates by reactive molecular-beam epitaxy. Enhancement of the N\'eel temperature by 1 K with 0.9$%$ compressive strain was revealed. The polar phonons of the films have been investigated as a function of temperature and magnetic field by means of infrared reflectance spectroscopy. All three in-plane polarized infrared active phonons show strongly stiffened frequencies compared to bulk EuTiO${}_{3}$ in accordance with first-principles calculations. The phonon frequencies exhibit gradual softening on cooling, leading to an increase in static permittivity. Additional polar phonon with frequency near the TO1 soft mode was detected below 150 K. This mode coupled with the TO1 mode was assigned as the optical phonon from the Brillouin zone edge, which is activated in infrared spectra due to an antiferrodistortive phase transition and due to simultaneous presence of polar and/or magnetic nanoclusters. In the antiferromagnetic phase, we have observed a remarkable softening of the lowest-frequency polar phonon under an applied magnetic field, which qualitatively agrees with first-principles calculations. This demonstrates the strong spin-phonon coupling in EuTiO${}_{3}$, which is responsible for the pronounced dependence of its static permittivity on magnetic field in the antiferromagnetic phase.

Frozen-in trans and gauche conformational disorder of symmetrical difluorotetra-chloroethane (DFTCE) produces the tendency of this plastic crystal to form an orientational glassy state on cooling below Tg=86 K. To throw light upon the freezing mechanism in DFTCE neutron diffraction and Brillouin scattering as well as infrared and dielectric measurements are employed. The overall picture of the results obtained can be characterized in terms of a classical glass-transition process with a relaxation frequency obeying the Vogel-Fulcher law. However, a more sophisticated picture of the freezing process is indicated by a quantitative analysis of the new Brillouin data, e.g. the temperature dependence of the sound velocity. The behaviour could be understood on the basis of a mode-coupling theory.

Far-infrared and near-millimetre dielectric response of Rb0.75(ND4)0.25D2PO4 (DRADP-25) has been determined by evaluation of reflectivity (30-650 cm−1) and complex transmittance (9-23 cm−1) spectra at temperatures of 10-300 K. In addition to polar phonons, the submillimetre response shows an overdamped soft mode like in DRADP-50. Due to this soft mode, the low-frequency dielectric data (104-107Hz) show a broad permittivity maximum near 145 K. Another lower-frequency dispersion, specific for the dipolar glass phase, was observed below 100 K.

In this first contribution to The Retrospective File, the former Director of the National Archives of Zimbabwe looks back over ten years of achievement.

Polarized microscope observation of ferroelastic domains in a SrBi2Ta2O9 (SBT) single crystal reveals the presence of domains up to Tc1≃770 K, which supports the ferroelasticity and Amam symmetry of the intermediate phase between ferroelectric and paraelectric phases. Far-infrared spectra of SBT ceramics, single crystal and thin films show a well underdamped optical soft mode at 28 cm−1, which partially softens to 21 cm−1 near the ferroelectric transition temperature (Tc2≅600 K). This softening does not explain the entire anomaly of low-frequency permittivity observed near Tc2. On the basis of high-frequency measurements, which do not show a significant dispersion, central-mode-type dispersion in the 10–100 GHz range is proposed as an explanation. So, the phase transition at Tc2 apparently shows a crossover behavior between the displacive and the order–disorder type.

Terahertz and far-infrared electric and magnetic responses of hexagonal piezomagnetic YMnO3 single crystals are investigated. Antiferromagnetic resonance is observed in the spectra of magnetic permeability mu_a [H(omega) oriented within the hexagonal plane] below the Neel temperature T_N. This excitation softens from 41 to 32 cm-1 on heating and finally disappears above T_N. An additional weak and heavily-damped excitation is seen in the spectra of complex dielectric permittivity epsilon_c within the same frequency range. This excitation contributes to the dielectric spectra in both antiferromagnetic and paramagnetic phases. Its oscillator strength significantly increases on heating towards room temperature thus providing evidence of piezomagnetic or higher-order couplings to polar phonons. Other heavily-damped dielectric excitations are detected near 100 cm-1 in the paramagnetic phase in both epsilon_c and epsilon_a spectra and they exhibit similar temperature behavior. These excitations appearing in the frequency range of magnon branches well below polar phonons could remind electromagnons; however, their temperature dependence is quite different. We have used density functional theory for calculating phonon dispersion branches in the whole Brillouin zone. A detailed analysis of these results and of previously published magnon dispersion branches brought us to the conclusion that the observed absorption bands stem from phonon-phonon and phonon- paramagnon differential absorption processes. The latter is enabled by a strong short-range in-plane spin correlations in the paramagnetic phase., Comment: subm. to PRB

The relaxor ferroelectric PbMg1/Nb2/3O3 was investigated by means of broad-band dielectric and Fourier Transform Infrared (FTIR) transmission spectroscopy in the frequency range from 1 MHz to 15 THz at temperatures between 20 and 900 K using PMN films on infrared transparent sapphire substrates. While thin film relaxors display reduced dielectric permittivity at low frequencies, their high frequency intrinsic or lattice response is shown to be the same as single crystal/ceramic specemins. It was observed that in contrast to the results of inelastic neutron scattering, the optic soft mode was underdamped at all temperatures. On heating, the TO1 soft phonon followed the Cochran law with an extrapolated critical temperature equal to the Burns temperature of 670 K and softened down to 50 cm-1. Above 450 K the soft mode frequency leveled off and slightly increased above the Burns temperature. A central mode, describing the dynamics of polar nanoclusters appeared below the Burns temperature at frequencies near the optic soft mode and dramatically slowed down below 1 MHz on cooling below room temperature. It broadened on cooling, giving rise to frequency independent losses in microwave and lower frequency range below the freezing temperature of 200 K. In addition, a new heavily damped mode appeared in the FTIR spectra below the soft mode frequency at room temperature and below. The origin of this mode as well as the discrepancy between the soft mode damping in neutron and infrared spectra is discussed.

Polarized infrared reflectivity was measured between 5 and 300 K on a 17 nm thick, 1.1% compressively strained epitaxial (001) SrTiO(3) film and the orthorhombic (110) NdGaO(3) substrate upon which it was grown. A strong in-plane infrared anisotropy of the NdGaO(3) substrate was observed and polar modes with B(1u)-and a mixture of B(2u) + B(3u)-symmetry were seen. At low temperatures three new modes arose in the 90-130 cm( - 1) range, which we assigned to 4f Nd electronic transitions. The in-plane SrTiO(3) film phonons showed strong stiffening compared to the phonon frequencies of bulk unstrained SrTiO(3), particularly the soft mode, and the in-plane phonon peaks were found to split. No anomalies were detected as a function of temperature in either the infrared response or lattice parameters of the compressively strained SrTiO(3) film, providing an absence of evidence for the out-of-plane ferroelectric phase transition predicted by theory.

Magnesium titanate (MgTiO3) powder was prepared by a chemical route (Pechini method) and different dopants were added to prepare several compositions. These pure and doped compositions were sintered in air and dense ceramics were obtained. The pure MgTiO3 samples were also subjected to different heat treatments during sintering. Complex permittivity spectra of ceramic samples were determined by various techniques in the 109–1014 Hz range. These techniques included infrared spectroscopy in transmission and reflectivity modes and microwave dielectric measurements. Extrapolation to microwave frequencies from infrared data, according to the proportionality ɛ″(v) ∝ v, agrees quite well with the microwave data measured at 8 GHz and it is a useful procedure to estimate intrinsic microwave losses. Fast cooling from high temperatures of MgTiO3 samples increased dielectric loss, probably due to a structural disorder. Dopants have two types of effect depending on whether they form a distinct second phase or a solid solution with MgTiO3. In this last case intrinsic losses are strongly affected.

The far-infrared and near-millimetre dielectric response of Rb0.5(ND4)0.5D2PO4 (DRADP) has been determined by evaluation of reflectivity (15-650 cm-1) and complex transmittance (5-18 cm-1) spectra at temperatures of 10-300 K. Comparison with the response of Rb0.5(NH4)0.5H2PO4 (RADP) shows a very pronounced isotopic effect and strong coupling of the proton motion to several polar phonon modes apparently reduced in the case of deuterium. Also the broad background absorption observed previously in RADP is absent in DRADP, which suggests an important role of quantum tunnelling in the former case. The loss maxima due to acid deuteron hopping (including lower-frequency data from He) in the broad temperature range 300-60 K can be well fitted with the Vogel-Fulcher dependence (TVF approximately=34 K, E0=410 K, vinfinity =1.2*1012 Hz). However, in agreement with several other experiments, above approximately 120 K the deuteron mode is monodispersive and the Debye relaxation frequency within the accuracy limits also obeys the Arrhenius law (E0=500 K, vinfinity =1.2*1012 Hz).

International audience; The long-standing classification scheme of ferroelectrics into either relaxor or displacive ones (the phase transition is driven by a soft phonon mode) is too restrictive since a smooth crossover between them exists which even admits for a coexistence of both phenomena. This crossover and coexistence is a consequence of the varying density of polar nanoregions due to different doping levels of the respective system. The formation of polar nanoregions is attributed here to intrinsic local modes in terms of discrete breathers.

All three components of the dielectric constant of KSCN have been measured in the frequency range 103–107 Hz and 1011–1012 Hz in a wide temperature interval around and below the order-disorder transition at 415 K. The increase of the low frequency permittivity e i (T) (i = a, b, c) with temperature T is correlated to the appearance of the disorder near the transition with the law (1/χ i (T) - 1/χ i (B) α Q 2(T) where 1/χ i (B) is the background permittivity extrapolated from the high-temperature phase and Q is the order parameter. The origin of the anomaly are the submillimetre and millimetre absorption processes induced by the disorder. The low-frequency dielectric losses above room temperature are dominated by ionic conduction.