The contribution of domain walls to the small-signal complex permittivity of BaTiO3

A method is proposed for determining the contribution _w of 180° domain walls to the initial permittivity of ferroelectrics. It consists in measuring the dependence of on the mean polarization of the sampleP _a at a frequencyf>f _r , wheref _r in the case of BaTiO₃ denotes the basic resonance frequency of thickness vibrations. It is shown that the measurements of Meitzler and Stadler [7] and our measurements prove the existence of _w in the regionf _r 3 crystal _w =15 to 30, _w =1 to 5. The existence of _w for low frequencies (f _r ), where the clamping effect occurs [6], is discussed.The author is indebted to O. Sedmík and V. Janouek for help in the measurements. He also thanks Dr. A. Fousková and Dr. V. Janovec for stimulating discussions and Dr. V. Dvoák and Dr. J. Kaczér for valuable remarks on the paper.     

Manifestation of circular photogalvanic current by dynamic holography in BaTiO3

We report the first measurement of the photo-galvanic circular current antisymmetric tensor component in BaTiO₃: Co. The measurement gives a value of this coefficient, for extraordinary beam amplification, of 4×10^–9 A/W using a nonstationary measurement technique at a wavelength of 0.632 m.Professor N. Kukhtarev is on leave from the Institute of Physics in the Ukraine and is supported by the NSFDr. G. Dovgalenko is on leave from the IRPA Rotor-Control research laboratory of the Ukraine and is supported by the University of Arkansas     

The electron paramagnetic resonance in reduced BaTiO3 crystals

The electrcn-spin resonance of reduced BaTiO₃ crystals, which was studied by Z. roubek and K. d'ánský [Czech. J. Phys.B 13 (1963), 309], is interpreted as the resonance of the Ti³⁺ ion. The facts which favour this interpretation are discussed. The distortion of the oxygen ions surrounding the Ti³⁺ ion has been taken into account in order to explain the measured electron paramagnetic resonance spectrum. Considering the crystal-field model of C_4v point-group symmetry, the Stark energy-level separations of the Ti³⁺ ion and the values of theg factors are calculated.The authors would like to thank Dr. E. imánek for many very helpful discussions and Dr. H. Arend for helpful comments.     

Diffusion Induced Grain-Boundary Migration and Enhanced Grain Growth in BaTiO3

The effect of diffusion induced grain-boundary migration (DIGM) on grain growth has been studied in a model system of BaTiO₃-PbTiO₃. When sintered BaTiO₃ samples of two different grain sizes were heat-treated in contact with PbTiO₃, DIGM occurred in the coarse-grained samples (200 m in average size) while fast grain growth was observed in the fine-grained samples (4 m). Energy dispersive spectroscopy (EDS) analysis confirmed that the fast growth of BaTiO₃ grains was accompanied by the alloying of Pb and thus related to DIGM. A calculation of coherency strain energy for the BaTiO₃-PbTiO₃ system showed that the coherency strain energy of a coherent (Ba_0.8Pb_0.2)TiO₃ layer on BaTiO₃ was between 2 and 3 MJ/m³ depending on the surface orientation. The calculated coherency strain energy values are much higher than the capillary energy due to the grain boundary curvature of 4 m grains in the fine-grained sample. The observed enhancement of grain growth appears therefore to be a result of DIGM. Such grain growth enhancement by DIGM is thought to occur in materials processing under chemical inhomogeneity or inequilibrium, for example, in the sintering of powder mixtures and in the annealing of chemically inhomogeneous polycrystals.     

Growth and characterization of (001)-oriented Pb(Zr0.52Ti0.48)O3/LaNiO3/LaAlO3 heterostructures prepared by pulsed laser deposition

Completely (001)-oriented ferroelectric Pb(Zr_0.52Ti_0.48)O₃/LaNiO₃ heterostructures on single-crystal LaAlO₃(001) substrates have been successfully grown by pulsed laser deposition. X-ray-diffraction analyses (–2 scan, scan and scan) indicate that good out-of-plane orientation and in-plane alignment have been obtained with the epitaxial relationship of PZT(001)//LNO(001)//LAO(001) and PZT001//LNO001//LAO001. Scanning electron and atomic force microscopic images reveal very smooth LNO surfaces with roughness of about 0.4–0.6 nm. Based on a microstructural study of the LNO and PZT films, a layer-by-layer growth mode for the LNO growth is proposed, while island growth is dominant for the PZT films. Secondary ion mass spectroscopy analyses show that no distinct interdiffusion can be found between the PZT and LNO layers. P–E hysteresis loop measurements of the PZT films with LNO as bottom electrodes and Au as top electrodes were carried out at an applied voltage of 5 V. The best remanent polarization P_r and coercive field E_c were found to be 28 C/cm² and 74.5 kV/cm, respectively. PACS 81.15.Fg; 68.55.Jk; 77.22.Ej; 77.84.Bw; 68.65.Ac     

Anti-parallel ferroelectric domains in surface space-charge layers of BaTiO3

It is shown on simplified models of a surface space-charge layer of a single crystal of BaTiO ₃ that in the surface region, in which the direction of the electric field is opposite to the direction of spontaneous polarization inside the crystal, anti-parallel domains can exist. The dimensions of these domains are determined. The use of the results obtained is proposed for interpreting the microrelief of the etch figures and for explaining the different phases of the polarization reversal process of a single-domain single crystal of BaTiO ₃.

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BatiO₃

BaTiO₃ , , , . . BaTiO₃.

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The author would like to thank J. Kaczer, Z. Málek and V. Dvoák of the Institute of Physics, Czechoslovak Academy of Sciences, for valuable remarks on this paper and H. Havlíková for carefully carrying out the numerical calculations.     

Measurement of the refractive index and optical absorption spectra of epitaxial bismuth substituted yttrium iron garnet films at uv to near-ir wavelengths

Refractive-index and optical-absorption spectra of Bi-substituted yttrium iron garnet films, epitaxially grown by liquid-phase epitaxy, have been measured in the spectral regime 0.26 m1.9 m by thin-film interference for 0.52 m and by ellipsometry for0.52 m. The Y_3–x–y Bi _x Pb _y Fe_5–z Pt _z O₁₂ films contain bismuth in the range Ox 1.42, lead in the range 0.01 y0.08 and platinum in the range 0.005<=z0.03. There is satisfactory coincidence between the results from ellipsometry and thin-film interference in the overlapping wavelength region. The materials investigated are the same as reported earlier from this laboratory in ter mof their magnetic and magnetooptic properties.     

Colour centre in BaTiO3 single crystals

The position of the absorption band of a colour centre formed by one electron trapped on an oxygen vacancy, in a cubic modification of BaTiO₃ single crystals, is quantum mechanically calculated.

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BaTiO₃

- , , , BaTiO₃.

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In conclusion the author thanks Dr. M. Trlifaj, corresponding member of the Czechoslovak Academy of Sciences, for valuable suggestions and remarks. He also thanks Dr. H. Arend, B. Bezina, C. Sc., P. Coufová and V. Janovec, C. Sc., of the Institute of Physics, Czechoslovak Academy of Sciences, for helpful discussions.     

Preparation of epitaxial compositionally graded (Ba1-xSrx)TiO3 thin films with enhanced dielectric properties

Epitaxial compositionally graded (Ba_1-xSr_x)TiO₃ (BST) (0.0x0.25) thin films were deposited on (100) LaAlO₃ substrates by pulsed laser ablation, the substrates having bottom electrodes made of 100-nm-thick conductive La_0.5Sr_0.5CoO₃ (LSCO). Extensive X-ray diffraction, rocking-curve, and -scan studies indicate that the graded films are (100)-oriented and exhibit good in-plane relationships of [010]_BST//[010]_LAO and [001]_BST//[001]_LAO. For the up-graded films with barium concentration (1-x) increasing across the film thickness in the direction from the film/substrate interface to the film surface, the full width at half maximum of the BST film (200) rocking curve and the surface roughness, examined by atomic force microscopy, were larger than those of the down-graded films with barium concentration decreasing from the film/substrate interface to the film surface. The dielectric properties of the graded films, measured using vertical structures, show that at room temperature, the dielectric constant (_r) and dissipation factor (cos) at 100 kHz were 380 and 0.013 for the up-graded films, and 650 and 0.010 for the down-graded films, respectively. The dielectric behavior was enhanced in the down-graded films, which was attributed to the fact that the pure BaTiO₃ layer in the down-graded BST films not only serves as a bottom layer but also acts as an excellent seeding layer for enhancing subsequent film growth, leading to better film crystallinity and larger grain sizes in the down-graded films. The graded BST films undergo a diffuse phase transition, giving a broad, flat capacitance-versus-temperature profile. With such a graded structure, it is possible to build a dielectric thin-film capacitor having a capacitance which has a low temperature dependence over a broad temperature regime. PACS 77.55.+f; 68.55.Jk; 81.15.Fg     

Singularities of ferroelectric properties of BaTiO3 crystals obtained with different crystallization rates

Ferroelectric properties are investigated of BaTiO₃ particles as a function of their growth rates. This latter was given as the rate of reduction of the temperature = dT/dt of the mother solution BaTiO₃-KF and varied between the limits 3.6–43 K/h. It is established that as a grows the reversible macroscopic polarization P_m diminishes according to the law , where P_m0 = 22·10^–2 C/m² and k = 6·10^–2 h/K. The coercive force E_c increases here while the domain contribution to measured in weak fields diminishes. It is shown that diminution of the growth rate results in improvement of the reverse polarization characteristics of BaTiO₃ crystals, a rise in the efficiency of their mono-domainization that would permit utilization of crystals obtained for = 3.6 K/h for optical purposes.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 76–78, November, 1990.     

Effect of bias field on the dielectric properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals with different orientations

Microdomain-macrodomain transformations and phase transitions in 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ single crystals were investigated by studying their relative permittivity under various dc bias at constant heating and cooling rates. The orientation dependence of the bias field effect was revealed by examining the temperature dependence of relative permittivity as a function of crystal orientation (the 111, 011 and 001 directions) and dc bias field. The crystals have a microdomain rhombohedral ferroelectric state in the ferroelectric phase under zero dc bias. External bias field could modulate the domain state and induce a macrodomain state in the crystals. Also, it is proposed that the dc bias applied along the 001 or 011 direction could induce a tetragonal ferroelectric phase or an orthorhombic ferroelectric phase, respectively, in an intermediate temperature range. PACS 77.80.-e; 77.22.-d; 81.40.-z     

Measurement of superhigh-frequency dielectric permittivity for paraelectrics (Ba,Sr) TiO3 in a transverse bias field

An improved apparatus for measuring dielectric permittivity in the shf range by the dielectric-resonance method is described. A cylindrical sample is placed at the antinode of a waveguide magnetic field. A measurement-line probe, placed at the minimum of the standing wave, is used to indicate resonance. Dielectric resonances are traversed by varying the sample temperature and dielectric permittivity. Results of measuring temperature dependences of and tan are given for BaTiO₃ ceramics and BaTiO₃ SrTiO₃ solid solutions in the paraelectric phase. The dependences of on a bias electric field perpendicular to the measuring field are found. It is shown that in a transverse bias field decreases though to a smaller extent than in a longitudinal field. It is concluded that the basic mechanism of paraelectric nonlinearity is the saturation of electron-ion polarization.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 9, pp. 20–25, September, 1971.     

On the interpretation of the thickness dependence of the coercive field of BaTiO3 single crystals

It is shown in the paper that the thickness dependence of the coercive field of unetched and of successively etched BaTiO₃ single crystals can be explained by the presence of a ferroelectric surface layer with decreased permittivity. In contrast to the Merz model [1], which considered a homogeneous layer, the authors assume that the permittivity inside the layer gradually decreases in the direction to the surface. By using experimental results it has been found for the constant, characterizing (according to [1]) the thickness dependence of the coercive field of unetched crystals, that=1.6 V, which is in satisfactory agreement with experiment.The authors thank V. Dvoák C.Sc, J. Fousek C.Sc, and Z. Málek C.Sc. for stimulating discussions.     

Pulsed-laser deposition of inclined ZnO, of GaPO4 and of novel composite thin films

Pulsed-laser deposition of different novel thin film materials is reported. Pure ZnO, Al-doped and Li-doped ZnO thin films and double-layers with inclined crystal orientation and very strong texture were achieved. The inclined ZnO heterostructures consisted of pure and doped layers of strongly different electrical resistivity. Polycrystalline GaPO₄ thin films were grown by F₂-laser ablation of ceramic GaPO₄. Layers of a novel composite material were produced from BaTiO₃/polytetrafluoroethylene mixed targets. The composite films revealed a giant dielectric permittivity, _r 15000, and a strong dependence of permittivity on the thickness of the layers. PACS  61.10.-i; 68.37.-d; 81.15.Fg     

Effect of Mg doping on the structural and dielectric properties of strontium titanate ceramics

The influence of Mg incorporation into A- and B-sites of the perovskite lattice of SrTiO₃ ceramics on the structural, microstructural and low-frequency dielectric properties is studied in this work. Compounds in the systems Sr_1-xMg_xTiO₃ and SrTi_1-yMg_yO_3- were synthesised by a conventional solid-state method. The solid solubility of Mg is restricted to x<1% for A-site occupancy (Sr_1-xMg_xTiO₃) and to y<15% for B-site occupancy (SrTi_1-yMg_yO_3-). The lattice parameter is found to increase with Mg content for the SrTi_1-yMg_yO_3- system, while it is almost invariant in the Sr_1-xMg_xTiO₃ one. The dependence on the lattice-site occupancy is also verified for the grain growth of ceramics. For SrTi_1-yMg_yO_3- the average grain size markedly decreases with increasing Mg content. For Sr_1-xMg_xTiO₃ the inverse dependence is observed. Contrary to expectations, Mg does not induce ferroelectricity or relaxor-like behaviour in strontium titanate, located in either A- or B-sites of the SrTiO₃ lattice. Moreover, fitting the dielectric behaviour to Barretts law demonstrates that B-site doping drives the system away from the ferroelectric instability. In Mg-doped strontium titanate ceramics the dielectric permittivity and dielectric losses decrease. The results are discussed based on the correlation between cation-site occupancy, charge and chemical stoichiometry in both systems. PACS 61.10.Nz; 68.37.Hk; 68.37.Lp; 77.22.Ch; 77.22.Gm; 77.84.Dy     

Light-induced charge transport in BaTiO3 via three charge states of rhodium

By combined studies of electron spin resonance and optical absorption at low temperatures, the charge-transfer bands of Rh⁵⁺ and Rh⁴⁺ are identified to be peaked near 1.6 and 1.9 eV, respectively. On this basis, the light-induced charge-transfer processes in BaTiO₃:Rh are unraveled at room temperature. It is shown that three charge states of Rh are involved, leading to two levels: the shallow Rh^4+/5+ and the deeper Rh^3+/4+ level. The optical behaviour of these two levels corresponds to those expected from a two-center model. The present paper represents the first atomic-scale identification of three charge states of one element leading to optical two-level response.     

Magnetoresistance in two-dimensional magnesium films of various thicknesses

The magnetoresistance of thin magnesium films in the weakly localized regime has been measured at 4.2 K as a function of film thickness. The results are analysed in a new and simple way based on the theory of Hikami et al. [1]. We use only two adjustable parameters, the inelastic relaxation time _i and the spin-orbit scattering time _so. Whereas _so is found to be almost independent of thickness, _i changes significantly. The variation of _i with thickness is discussed in the light of the theories for the enhanced electron-electron interaction, but it does not seem to tie up with any of the existing theories.     

Relationship between low frequency dielectric dispersion and ferroelectric phase transition in pulsed-laser-deposited Bi<Subscript>4-x</Subscript>La<Subscript>x</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin film

The frequency and temperature dependence of the complex dielectric constant of Bi_4-xLa_xTi₃O₁₂ (BLT, x=0.9) ferroelectric thin film was studied in the frequency range of 10^-110⁶ Hz and the temperature range of 298673 K. A low frequency dielectric dispersion (LFDD) was found. A model was proposed to account for this observed phenomena. The complex dielectric constant data obtained in the measured frequency and temperature ranges have been found to fit very well to the dielectric dispersion relation: ^*=+i/₀+[B(i)^n-1]/₀. The knee in the log of the electrical conductivity versus the reciprocal temperature curve occurs at T_c. The activation energies associated with charge conduction are E_a,II=0.73 eV below T_c and E_a,I=0.95 eV above T_c. The occurrence of an anomaly in both the n and parameters near T_c indicates a coupling between charge carries and phonons. PACS 77.55.+f; 77.80.-e; 77.22.Jp     

On surface layers on BaTiO3 single crystals

The possibility of explaining the existence of a surface layer on BaTiO₃ crystals by the presence of Schottky defects in the crystal is investigated. The magnitude of the potential difference between the surface and the interior of the crystal and the thickness of the surface layer, which at temperatures of over 400°C agrees with the measured values, are calculated for the cubic phase from a simplified ionic model.

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BaTiO₃

iO₃ . , 400° .

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In conclusion the author would like to thank Dr. M. Trlifaj and V. Janovec, candidates of physics and mathematics, for valuable remarks.     

On the electric conductivity of BaTiO3 thin films

Results are presented of tests on the conductivity of BaTiO₃ and Ba(Ti, Sn)O₃ films obtained by various techniques and thickness order 1–100 m. Studies on electrical photoconductivity were conducted using ultraviolet radiation.The author wishes to thank R.Dytry, J.Genbar, J.Pawlik and R.Skulski for help in the experiments.