Temperature Dependence Of Dielectric Response Research Articles

Исследование диэлектрического отклика, проводимости и тока термостимулированной деполяризации в релаксорном сегнетоэлектрике PbNi-=SUB=-1/3-=/SUB=-Nb-=SUB=-2/3-=/SUB=-O-=SUB=-3-=/SUB=-

This paper presents results of a study of temperature dependences of dielectric response and DC and AC - conductivity in single crystals of the relaxor ferroelectric PbNi1/3Nb2/3O3 (PNN) in a wide range of frequencies (10 Hz - 100 kHz) and temperatures (80 - 750 K). Anomalies in the dielectric response in the form of broad frequency-dependent maxima in the vicinity of 153 and 730 K are observed. The thermal activation character of DC conductivity has been obtained, and activation energies determined as Ea = 770 meV (T > 310 K) and Ea = 23 meV (T <310 K). The analysis of conductivity gives reason to assume the existence of local conductivity in the low-temperature region. It is shown that the conductivity character changes above 350 K from the local to the bulk one. Measurement by thermally stimulated depolarization has shown the presence of a residual polarization below 130 K.

Structure and microwave dielectric properties of epitaxial 0.7CaTiO3-0.3NdAlO3 dielectric thin films deposited by pulsed laser deposition

High quality epitaxial 0.7CaTiO3-0.3NdAlO3 (CTNA) dielectric thin films with complex perovskite structure are deposited on SrTiO3 substrates by pulsed laser deposition. In a combination with XRD and aberration-corrected TEM, the strain state and oxygen octahedral rotation are analyzed in detail. The substrate temperature dependence of microwave dielectric properties has been investigated by a split-post dielectric resonator method. The dielectric constant and dielectric loss tangent of the CTNA thin film deposited at 700 °C are 417 and 0.048 at 10 GHz, respectively. The dielectric response of CTNA films derived from far-infrared reflectance spectroscopy shows that the frequency of phonon mode TO1 centered at 174.5 cm−1 is shifted to 176.6 cm−1 with increasing substrate temperature. In contrast, the damping factor decreases with increasing substrate temperature. The substrate temperature dependence of dielectric response mainly results from the strain-induced oxygen octahedral rotation.

Magnetic and dielectric properties of o-LuFeO3/SrTiO3

Here we present the investigation of the orthorhombic o-LuFeO3 thin film grown on SrTiO3 (001) substrate. Temperature dependencies of magnetization measured in magnetic fields 1000 Oe and 2000 Oe were described in the assumption that ferromagnetic correlated regions are presented in samples together with the paramagnetic phase. Additional argument in favor of the ferromagnetic regions existence in o-LuFeO3 is the magnetic hysteresis curve measured at T=5 and 100K. The temperature dependences of dielectric response were measured and analyzed.

Microwave and broadband dielectric properties of Ni substituted MgTiO3 ceramics

The present study reports the temperature dependence of dielectric response of Ni doped MgTiO3 ceramics over a broad frequency range. (Mg1−xNix)TiO3 (x = 0.00–0.07) ceramics are prepared by a solid-state reaction process. The processing parameters are optimized to achieve maximum relative density. Among all the samples, (Mg0.95Ni0.05)TiO3 (MNTO) ceramics is exhibited the highest density with the best microstructure at 1300 °C. The optimum microwave dielectric properties (er ~ 17.44, Q × f0 ~ 181 THz) are displayed by the sample doped with x = 0.05 wt%. The detailed dielectric studies are performed on (Mg0.95Ni0.05)TiO3 composition in two different frequency ranges, 100 Hz–100 kHz at 298–358 K and 1–100 MHz at 133–503 K, respectively. A dielectric constant of 18.26 at 100 MHz is observed for (Mg0.95Ni0.05)TiO3 specimen at temperature 503 K. The frequency dependent conductivity is explained based on the basis of Jonscher power law. Further, the DC conductivity results obey the Arrhenius law, and the obtained activation energies are found to be 0.41 and 0.06 eV for (Mg0.95Ni0.05)TiO3 ceramics, measured at 100 MHz for high temperature (293–503 K) and cryogenic temperatures (133–293 K), respectively.

Dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites of BaTiO3 and 0.975BaTiO3–0.025Ba(Cu1/3Nb2/3)O3

In this paper, we report the dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites consisting of BaTiO3 (BT) and 0.975BaTiO3–0.025Ba(Cu1/3Nb2/3)O3 (BTBCN). Two types of graded bilayer samples were synthesized, one with same thickness of BT and BTBCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BTBCN layers of equal thickness. Scanning electron microscopy and transmission electron microscopy images showed a sharp interface with needle-shape domains across the interface. The domain size on BT side was found to be larger than that on BTBCN side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting in characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BTBCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from polarization-electric field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area ⟨A⟩, Pr, and EC decreased with increasing frequency due to delayed response but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations.

Effect of Sm Substitution on Structural, Dielectric, and Transport Properties of PZT Ceramics

The polycrystalline samples of Pb1−xSmx (Zr0.45Ti0.55)1−x/4O3 (PSZT) (where x = 0.00, 0.03, 0.06, and 0.09) were prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the materials at room temperature has confirmed their formation in single-phase with tetragonal crystal structure. The temperature dependence of dielectric response of the samples at selected frequencies has exhibited their phase transition well above the room temperature. The variation of ac conductivity with temperature and the value of activation energy reveal that their conduction process is of mixed type (i.e., singly ionized in ferroelectric region and doubly ionized in paraelectric phase).

Microstructural and electrical study of mixed phase of Pb(Ba 1/3Nb 2/3)O 3

A new lead-based relaxor Pb(Ba 1/3Nb 2/3)O 3 (PBN), synthesized by a columbite route, is reported. X-ray diffraction shows a perovskite structure with a small percentage of cubic pyrochlore phases. Temperature dependence of dielectric response shows the typical relaxor behavior. Impedance spectroscopic data were used to gain an insight into the electrical properties of the sample.

Dynamical Properties of the Partially Disordered Crystals of Cs 5 H 3 (SO 4 ) 4 · x H 2 O

This paper presents studies of lattice dynamics of a crystal of Cs 5 H 3 (SO 4 ) 4 x H 2 O (PCHS) and its deuterated analog Cs 5 D 3 (SO 4 ) 4 x D 2 O (DPCHS) in wide temperature and frequency ranges by dielectric spectroscopy and modulated temperature differential scanning calorimetry. It is shown that deuteration of PCHS gives rise to an additional structural phase transition at T c3 , 250 K. The temperature of the isostrctural phase transition T c2 (372 K for PCHS and 370 K for DPCHS) has been determined more accurately. It has been found that deuteration does not suppress phase transition at T c2 . The temperature dependence of dielectric response is analyzed.

Optical Properties and Model of Relaxor Ferroelectrics

Phenomenological approach to a relaxor theory is developed and some experi-mental results in the support of this theory are received. The optical absorption spectrum, luminescent emission and photoconductivity are investigated in the wide temperature region in PbMg 1/3 Nb 2/3 O 3 . On the basis of this data the density of states on the impurity band and the velocity of charge carrier localization are found. The probability distribution of relaxation time, g (ln( ))dln( ), is found analytically as the function of the density of states in the impurity polaron band. The temperature dependences of dielectric response of relaxor ferroelectrics are described in the framework of the Landau-Ginzburg-Devonshire theory of phase transitions. The properties of local centers and polaron localization dynamics are studied.

Anion-Deficient Perovskite Pb(Mg0.5Nb0.5)O2.75 Ceramics Obtained under High Pressure

Single phase ceramics with the composition Pb(Mg0.5Nb0.5)O2.75 (PMN-V) were prepared under high pressure and temperature conditions. Cubic perovskite phase of PMN-V with a lattice parameter a = 4.0495 ± 0.0003 Å was revealed to be stable at normal pressure up to 1120 K. Temperature dependence of dielectric response of the high-pressure sintered PMN-V ceramics showed two particular regions: a diffuse ferroelectric transition with the frequency independent maximum and a typical relaxor crossover at lower temperature. Effect of high-pressure and stoichiometry (oxygen vacancies) on the B-site cation ordering and dielectric behaviour of PMN is discussed.

Charge Localization in the Model of Relaxor Ferroelectrics

Phenomenological approach to a relaxor theory is developed and some experimental results in the support of this theory are received. The optical absorption spectrum, luminescent emission and photoconductivity are investigated in the wide temperature region in PbMg1/3Nb2/3O3. On the basis of this data the density of states on the impurity band and the velocity of charge carrier localization are found. The probability distribution of relaxation time, g(ln(τ))dln(τ), is found analytically as the function of the density of states in the impurity polaron band. The temperature dependences of dielectric response of relaxor ferroelectrics are described in the framework of the Landau-Ginzburg-Devonshire theory of phase transitions. We show that an additional condition for the relaxor behavior to appear is the coincidence of the phase transition temperature with the temperature region of thermo-localization of charges on the defects. The properties of local centers and polaron localization dynamics are studied.

Localized Charges and Model of Relaxor Ferroelectrics

Phenomenological approach to a relaxor theory is developed and some experimental results in the support of this theory are received. The optical absorption spectrum, luminescent emission and photoconductivity are investigated in the wide temperature region in PbM g 1/3 Nb 2/3 O 3 . On the basis of this data the density of states on the impurity band and the velocity of charge carrier localization are found. The probability distribution of relaxation time, g (ln( )) d ln( ), is found analytically as the function of the density of states in the impurity polaron band. The temperature dependences of dielectric response of relaxor ferroelectrics are described in the framework of the Landau-Ginzburg-Devonshire theory of phase transitions. The properties of local centers and polaron localization dynamics are studied.

Dielectric response of the alkaline earth fluorides

The temperature dependence of the low-frequency dielectric response of CaF2, SrF2 and BaF2 over the range 2-350 °k is reported, together with the pressure dependence, for hydrostatic pressures up to 5 kbar, at selected temperatures in the range 60 to 350 °k. The low-temperature data are used to assess the nature and extent of the electronic structure and interionic forces of the alkaline earth fluorides. The temperature dependence of the dielectric response is found to be due principally to intrinsic volume changes in the crystals rather than to intrinsic temperature changes in the anharmonic contribution. The temperature dependence under constant volume of the anharmonic contribution to the dielectric constant of all three salts exhibits a maximum value near 0·25 θD, where θD is the characteristic Debye temperature. The quasi-harmonic contributions are analysed to determine values for the κ similar, equals 0 longitudinal and infra-red active transverse optic phonon Gruneisen constants.