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Multiferroic composites with the general formula x BaTiO 3 –(1− x ) NiFe 2 O 4 ( x =0.5, 0.7, 0.8) were prepared by mixing chemically obtained nickel ferrite and barium titanate powders. Optimum processing parameters for a reduction of chemical reactions at the interfaces between ferroelectric-ferrite phases were found. The presence of the nickel ferrite and barium titanate single phases was detected by X-ray measurements. Good quality of the homogenized ceramics containing both phases was confirmed by use of scanning electron microscopy. Dielectric measurements showed the superposition of the multiple conductivity mechanisms responsible for the dielectric dispersion at frequencies up to 1 MHz. Calculated activation energies for DC conductivity showed the contribution of oxygen vacancies and Maxwell-Wagner related phenomena. Magnetic measurements of the composite materials were performed showing the coercivity increase and saturation of the magnetization moment decrease with the increase of barium titanate content.

For the first time results of the dielectric properties of PbCo 0.5 Ta 0.5 O 3 ceramics are reported in the frequency range of 200 Hz–1 MHz at temperatures 300–450 K. The frequency-dependent electrical data is discussed in the framework of the non-Debye relaxation using complex dielectric permittivity and electric modulus representations. The dielectric permittivity shows strong dispersion above room temperature with Arrhenius temperature dependent relaxation rate. The dielectric spectra at the low frequencies and at the high temperatures are highly influenced by the ionic conductivity. Frequency-dependent conductivity and non-Arrhenius mean electric relaxation time, obtained by the complex modulus M ⁎ ( ω ), are analyzed and similarities to ion glass state are pointed out.

Nondoped BiFeO3 (BFO) and doped Bi0.9La0.1Fe0.9Mn0.1O3 (BLFMO) thin films (d = 200–350 nm) were grown at 650–750 °C by RF sputtering on Si and SrTiO3(100), coated by conductive LaNiO3 films and La2/3Ca1/3MnO3/SrRuO3 bilayers. The complex dielectric permittivity of the films was measured at room temperature in the frequency range from 10 MHz to 10 GHz using parallel plate capacitor structures. Dielectric properties of the polycrystalline BFO films were compared with those of the epitaxial quality BLFMO films, and it was seen that the latter has better microwave performance than the former. The dielectric losses were below 0.05 at 1 GHz frequency, which may be acceptable for microwave applications.

The dielectric properties of CuInP 2 S 6 and Ag 0.1 Cu 0.9 InP 2 S 6 crystals were investigated in wide frequency (20 Hz-3 GHz) and temperature ranges (25-360 K). The low frequencies dielectric spectra at high temperatures are highly influenced by the high ionic conductivity. The temperature dependences of the static dielectric permittivity and the mean relaxation time reveal the first order order-disorder ferrielectric phase tran sition at T c = 288 K in Ag 0.1 Cu 0.9 InP 2 S 6 . The conductivity and its activation energy exhibit only a weak change close to the ferrielectric phase transition temperature in both investigated crystals. The freezing phenomena in CuInP 2 S 6 and Ag 0.1 Cu 0.9 InP 2 S 6 revealed the complex dielectric permittivity behaviour characteristic for transition into dipolar glass state.

In the present paper results of the dielectric investigation of barium titanate (BaTiO3) doped with different concentrations of lanthanum are presented. Ceramic samples were prepared by the Pechini process. With increased doping the grain size of ceramics decreases from 2.5 ?m in pure samples down to 0.2 ?m in 0.5 mol% La - doped BaTiO3. Ceramics showed maximally enhanced dielectric permittivity around low-, room and high temperature phase transitions, which are the phase transitions of the pure BaTiO3. The Curie temperature, TC, is lowered by 30 K with increase of doping concentration to 0.5 mol% La. Dielectric spectra revealed three parts: low frequency part which is caused by conductivity process, middle frequency relaxational process part and high frequency relaxational/polar modes contribution.

We report high frequency dielectric properties of multiferroic BiFeO3 (BFO) thin film deposited by means of aqueous chemical solution deposition on platinized silicon substrate. The structure analysis of the BFO performed by X-ray diffraction and energy dispersive analysis showed pure, single-phase quality of the thin films. The impedance measurements were performed by vector network analyzer in frequency range 100 MHz to 10 GHz at ambient temperature. The film leakage currents dominate dielectric losses at low frequencies. The dielectric constant of the film is around 40. An internal charged defects acting as energy traps for electrons dominate dielectric losses in the frequency region above 4 GHz. .

The dielectric/impedance spectra of Rb 3 H(SeO 4 ) 2 crystals has been studied in room- and high-temperature phases in wide frequency range. The original method of calculation of the distribution function g ( τ ) of relaxation times is applied for the ionic conducting materials. The high-frequency impedance spectrum splits into two relaxators by one order of magnitude at high temperatures. The calculated mean time for fast relaxation is 5.5 · 10 −9 s at T c = 450 K. The slower relaxation time is about ten times longer in the superionic phase. The difference between the faster and the slower relaxation times at high temperatures corresponds to the proportion of the rate of the proton transfer within hydrogen bond and that of the rotational hopping. The appearance of the two peaks in g ( τ ) confirms the two-stage transport mechanism in the hydrogen-bonded system and supports the theoretical suggestions of the important role of interproton interactions and the polaronic effect in superionic phase transition mechanism.

In this paper the results of dielectric spectroscopy of MCM-41 mesoporous material with incorporated MEOH are presented. Three dispersion regions of the confined MEOH have been found. The dielectric dispersion in the low temperature region is caused by MEOH molecules forming an interfacial layer with the inner surface of the mesoporous support. MEOH in the middles of the pores shows typical saddle like behaviour of the relaxation time. With incorporation of Al atoms in the framework of MCM-41 molecular sieves the saddle process becomes much weaker and vanishes at Si/Al = 64. Also, this process is followed by increase of conductivity.

The dielectric/impedance spectra of (NH4)3H(SO4)2 crystal has been studied in room- and high-temperature phases at frequencies up to 3 GHz. The results are analyzed by calculating the distribution function g(τ) of the relaxation times. The splitting of the spectrum into two relaxators on approaching phase transition temperature indicates possible two paths for protons contributing to conductivity in high-temperature phase. Results support idea of involvement in superionic transport of ammonium N(1)H4 protons along with protons in H-bonds between the apical oxygen atoms of sulfate tetrahedra.

This paper reports on an investigation on the light–current, relative intensity noise, and chirp variations of life-tested InGaAsP/InP multiquantum-well buried heterostructure (BH) laser diodes (LDs). The devices have been stressed at highly accelerated aging conditions ( $I = 170 hboxmA$ , $T = 140 ^circhboxC$ for 3000 h). Typically, the operating current at constant output optical power $(I_ op)$ increases logarithmically with time in stable devices while the noise resonance frequency remains stable. High-frequency RF signal-induced chirp for relative stable LDs at constant output power shows very little change with time.

The aim of the present work is to investigate newly sintered ceramics of gadolinium-substituted Aurivillius -type bismuth titanate, Bi 2.5 Gd 1.5 Ti 3 O 12 , by the impedance spectroscopy. The measurements were performed as a function of both frequency and temperature in the frequency range 20 Hz–1 MHz and in the temperature range 300 K–1050 K. The electrical conductivity and dielectric relaxation have been analyzed in terms of specific resistivity and electrical modulus. The onset of the ionic conductivity in the ceramic appears above the phase transition temperature, T 0 = 468 K. Activation energy for the conductivity was found to be ∆E A = 0.98 eV, while conductivity in grains has ∆E g = 0.93 eV.

Ionic conductivity of new rhombohedral compounds of Li 1+ x Y y Ti 2− y (PO 4 ) 3 system (where x , y =0.3; 0.4) has been investigated by impedance spectroscopy in the frequency range from 7×10 5 to 1.2×10 9 Hz at temperatures up to 600 K. The method of high frequency investigation of the electric parameters of the disordered materials is presented. The powder samples were synthesized by a solid phase reaction and studied by X-ray diffraction, which revealed changes in interplanar distances with change of x and y . Two relaxational dispersions of the electrical parameters were found and analyzed in terms of bulk and grain boundary ionic transport processes. The highest bulk conductivity σ b =0.18 S·m −1 with activation energy Δ E b =0.27 eV at room temperature was found for the compound with x , y =0.4 and these characteristics do not depend on sintering time of samples. The total ionic conductivity increase with number of Li + ions in the unit cell. The values of total ionic conductivity of the polycrystalline samples depend on time of sintering due to change of grain boundary resistance.

The paper presents the results of dielectric studies of the sequence of four phase transitions in AHSe crystals in the frequency range 100 Hz to 77 GHz, and ultrasonic studies in the range 10 to 70 MHz.

The dielectric behaviour of ferroelectric hydrogen-bonded deuterated betaine phosphite crystals is investigated in the frequency range up to 4 GHz. The dielectric dynamics of Debye type shows a critical slowing-down of the polarization fluctuations. The frequency of the relaxational soft mode in the para-electric phase varies according to v s = 0.2(T - 295.8) GHz and decreases to 0.55 GHz at T C = 298 K.

The results of study on dynamic dielectric properties of some H-bonded crystals are presented. It is shown that relaxational soft modes are responsible for the ferroelectric phase transition in RbD2PO4, PbHPO4 and NH4HSeO4 and their contribution accounts for the static permittivity. Glass-like dielectric relaxation with temperature depended relaxation time τ was observed in the ferroelastic phase of Cs5D3(SO4)4. Non-Debye dielectric relaxations characteristic to ionic conductors were observed in the high-temperature phases of Cs5D3(SO4)4 and NH4HSeO4.

This paper presents the results of an investigation of microwave dielectric dispersion in the semiconductive ferroelectric T1(InS2) 0.985 (FeSe2) 0.015 in the frequency range 1 MHz to 110 GHz. Dielectric dispersion did not give any evidence for the existence of an incommensurate phase in these crystals. It is shown that dielectric dispersion is Debye type in the frequency range 106 to 1011 Hz and is caused by two relaxational soft modes. The magnitude of the activation energy for the higher frequency relaxational mode is found to be U = 0.1 eV.

The paper presents the results of the dielectric investigations of the fundamental ferroelectric dispersion in the new or less studied order-disorder type organic-inorganic ferroelectrics.

The dielectric behaviour of ferroelectric hydrogen-bonded betaine phosphite crystals is investigated in the frequency range up to 77 GHz. The dielectric dynamics of Debye-type shows a critical slowing-down of the polarization fluctuations. The frequency of the relaxational soft mode in the paraelectric phase varies according to vs = 0.36(T-218) GHz and decreases to 2.4 GHz at Tc = 224 K. The calulated activation energy for flipping proton motion ΔU = 2.7kTc shows the order-disorder character of the proper ferroelectric phase transition. Betainphosphit ist ein Ferroelektrikum mit Wasserstoffbruckenbindungen. Im Frequenzbereich bis 77 GHz wird das dielektrische Verhalten eines Einkristalls untersucht. Die dielektrische Dynamik zeigt ein Debye-Verhalten mit einem kritischen “slowing-down” der Polarisationsfluktuationen. In der paraelektrischen Phase folgt die Frequenz der Relaxations-Softmode der Beziehung vs = 0,36 (T-218) GHz und nimmt bis zu 2,4 GHz ab. Die berechnete Aktivierungsenergie ΔU = 2,7kTc fur die Protonen-Bewegung belegt, das es sich um einen eigentlichen ferroelektrischen Phasenubergang vom Ordnung-Unordnungstyp handelt.

This paper presents the results of the investigation of the spontaneous polarization, dielectric anisotropy and dispersion in the new ferroelectric, dimethylammonium gallium sulphate. On cooling, the crystal undergoes two first-order phase transitions at T c1 = 136 K and T c2 = 106 K with the spontaneous polarization along the x-axis between T c1 and T c2. In the vicinity of T c1 the crystal shows a critical slowing down of polarization fluctuations. In the far paraelectric phase, ferroelectric dispersion of the Debye-type is caused by a single relaxational soft mode related to the flipping motion of the dimethyl-ammonium groups in a double well potential with an activation energy 0.09 eV = 7.6 kT c1 in the paraelectric phase. Near T c1 and in the ferroelectric phase the ferroelectric dispersion overlaps with the domain wall dispersion and causes a complicated dielectric spectrum.

The paper presents the results of the investigation of dielectric dispersion in monoclinic telluric acid ammonium phosphate crystal over the frequency range 1 MHz to 77 GHz. It is shown that ferroelectric dispersion of the Debye type along the direction perpendicular to the plane (101) occurs in the frequency range 108 to 1011 Hz and is caused by a single relaxational soft mode. The relaxational soft mode is caused by the flipping motion of protons between two potential minima in a hydrogen bond. The frequency of the flipping proton mode in the paraelectric phase varies according to vs = 0.94 (T – To ) GHz and decreases to 1.75 GHz at Tc = 317.3 K. The relaxational mode gives the main contribution to the high static dielectric permittivity of this crystal which fits the Curie-Weiss law. The results confirm the order-disorder nature of a proper ferroelectric phase transition of second order.

La- and Mn-doped multiferroic BiFeO 3 thin films were fabricated and characterized at radio- and microwave frequencies using the parallel-plate capacitor structures at a room temperature. A single phase epitaxial-quality thin films were grown by RF sputtering on SrTiO 3 (100) substrate with highly conductive SrRuO 3 and Ti/Au layers used as bottom and top electrodes. In the frequency range 40 MHz – 30 GHz the Bi 0.9 La 0.1 Fe 0.9 Mn 0.1 O 3 (BLFMO) films show relatively low losses and dielectric constant value close to 90. Analysis of the frequency dependences of loss tangent shows power law 1/3 with estimated value of microwave loss tangent less than 0.06 at frequencies below 20 GHz. We assume that the oxygen vacancies in the thin film act as charged defects and cause extrinsic microwave losses.

This paper presents the results of the investigation of dielectric dispersion and ultrasonic velocity in the ferroelectric (CH3)2NH2Al(SO4)2 · 6H2O crystal. The crystal shows a critical slowing down process of polarization with an extremely long relaxation time of the dipole system (τ = 1.6 · 10−7s at the phase transition point). The dielectric response over the frequency range up to 56 GHz in the paraelectric phase can be well described in terms of a monodispersive Debye-type formula. The activation energy of dipoles in the paraelectric phase is 0.11 eV = 8.5 kTc . The results show that the proper ferroelectric phase transition is nearly critical and of the order-disorder type.

In this paper, we report results on investigation of low-frequency optical and electrical noise spectra, as well as relative intensity noise (RIN), and their relation to the optical characteristics in a series of 1.55-/spl mu/m multiquantum-well strained-layer (SL) and buried-heterostructure (BH) DFB lasers subjected by an accelerated degradation procedure. We demonstrate the advantages of the use of the cross-spectra of low-frequency optical and electrical noise for quality and reliability evaluation of 1.55 /spl mu/m laser diodes. It is shown that optical and electrical noise correlation factor k is more sensitive for the lasers quality than noise intensity.

Dynamic characteristics of partly gain-coupled multiple-quantum-well InGaAsP distributed feedback laser diodes have been investigated. Basic dynamic parameters (differential gain, K-factor, differential carrier lifetime) were found out. It is shown that the increase of coupling coefficient results not only in both oscillation and damping frequency increasing, but also in time-resolved frequency chirp oscillation decreasing. Relation between K-factor and differential carrier lifetime and their correlation with deferential gain indicates essential differential gain role in dynamic parameter dispersion.

We present the dielectric dispersion in a Pb(Fe1/2Nb1/2)O3 (PFN) thin film grown on (001) SrTiO3 substrate from 20 MHz to 20 GHz in the temperature range of 270 to 340 K. In the radio frequency region, the hopping charge transport and associated polar nanoregion and/or domain-wall motion contribute to the spectrum. In the microwave region, relaxational dispersion was observed with a dielectric contribution of Δe ≈ 600 at room temperature having a characteristic frequency (fm)0.4 = 9.8 · (T−T0) Hz, where T0 is 660 K. It is associated with possible mode-softening behavior, related to the onset of polar nanoregions at T0. The dielectric permittivity shows similarities with 1-dimensional Ising model behaviour.

The paper presents the results of the investigation of the dielectric dispersion in diglycine nitrate crystals over the frequency range 1 MHz to 54 GHz. It is shown that the ferroelectric dispersion of the Debye type along the polar [101] direction is in the frequency range 108 to 1011 Hz and it is caused by the single relaxational soft mode. The frequency of the “flipping” proton mode in the paraelectric phase on approaching Tc varies according to γs = 0.34 (T - Tc ) GHz and makes the main contribution to the static permittivity which fits the Curie-Weiss law with the Curie constant C = 845 K. The magnitude of the activation energy of dipole reversal is found to be δU = 1.6 kTc . The results confirm the order-disorder type of ferroelectric phase transition.