Wyniki wyszukiwania - Biblioteka Nauki

1

Elevated temperature induced dispersion phenomena in Ba1-xNaxTi1-xNbxO3

100%

Bąk W. , Starzyk F. , Kajtoch C. , Nogas-Ćwikiel E.

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2008

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tom Vol. 29, nr 1

5-9

EN

Purpose: of this paper was to investigate features of the dispersion of dielectric permittivity induced by elevated temperature (473K-723K) in polycrystalline solid solution of Ba1-xNaxTi1-xNbxO3 (for x=0.3 and x=0.4). Design/methodology/approach: used to perform this purpose was dielectric spectroscopy application to measure dielectric and electric parameters within the frequency range (20Hz-1MHz). Findings: Analysis of temperature and frequency dependences of real (ĺ’) and imaginary (ĺ”) parts of dielectric permittivity had pointed out on relaxor type of dielectric behaviour for both investigated samples in paraelectric phase. The thermal activation energy values of ac conductivity (for 100Hz) are similar to those of semiconductors. Values of ĺ’ for both materials (x=0.3, x=0.4) are consistent with literature quotations. Thus the polarisation behaviour of our materials seems to be similar to those described in the literature. Different behaviour of dielectric energy losses is postulated as originating from differences of samples microstructure. Research limitations/implications: Further investigations should be carried out in the range of low temperatures (down to 100K) and within a broaden frequency range (up to 1.8GHz) in order to establish the influence of chemical structure on ferroelectric-paraelectric phase transition. Originality/value: Dielectric properties for two new material prepared from nanopowders of BaTiO3 and NaNbO3 were described.

2

Influence of electric field DC-component on AC-response of ferroelectric powder

100%

Starzyk F. , Bąk W. , Kajtoch C. , Gabryś M.

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2008

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tom Vol. 29, nr 1

36-39

EN

Purpose: of this work was to establish whether ac-response of freely stocked micro-granular ferroelectric matter on fringe measuring electric field depends on constant component presence VDC (or DC-Bias). Design/methodology/approach: used involves measurements of effective dielectric permittivity (and other effective dielectric quantities) by means of interdigit dielectrometry. Fringe measuring electric field was applied to BaTiO3 micro-powder by interdigit comb sensor (ICS) Netzsch of Ms25 type. ICS was driven by measuring generator with sinusoidal voltage: v(t)= VDC+VACsin(�ωt), within frequency range 20Hz-100kHz and for DC-Bias values ranging as VDC=(0-20)V. Findings: The interdigit dielectrometry was applied to measure complex dielectric permittivity, complex dielectric modulus and others dielectric functions of ferroelectric BaTiO3 powder. The influence of constant component of electric stimulus was investigated in the frequency range 100 kHz to 20 Hz. It was established that in the low frequency range constant component of electric field enhances effective dielectric permittivity, and changes two weak relaxation processes occurring in the ferroelectric micro-granular net. It turned out that effective dielectric complex modulus of this net is most sensitive quantity for application of constant component of electric stimulus. Research limitations/implications: The density solution effect is a source of small effective dielectric permittivity of micro-granular ferroelectric powder (�ε'). �Epsilon' values are being enhanced by presence of non zero VDC value. The same effect was established for effective energy loss coefficient (�ε"). The two relaxational processes connected with VDC�𕟀 seems to be a key feature of freely stocked ferroelectric matter. Originality/value: of this work relays on the fact, that this is a first report of the VDC influence on effective dielectric properties of ferroelectric micro-granular matter. It is opening the way to a new approach in modelling of effective dielectric properties of granular matter in nature and powders technology.

3

Study of phase transition specific in polycrystalline Pb(Cd1/3Nb2/3)O3

100%

Kajtoch C. , Bąk W. , Starzyk F. , Gabryś M.

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2008

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tom Vol. 29, nr 1

20-23

EN

Purpose: of this paper was to isolate and attempt to identify experimentally specific features of paraelectric diffused phase of Pb(Cd1/3Nb2/3)O3 (PCN) not reported yet in the literature. Design/methodology/approach: we used was to measure and analyse the temperature and frequency dependence of polarization, energy loss, phase angle and ac-conductivity components. Findings: we have isolated four specific processes visible as specific behaviour of ĺ’(T, í); on ĺ” and phase angle also temperature and frequency dependences and three contributions to ac-conductivity. Practical implications: processes isolated will be used to construct a model of polarizability and energy loss as well as ac-conductivity in diffused paraelectric phase of PCN. Originality/value: of the paper rely on the possibility of experimental verification of temperature induced evolution of polar regions structure and dynamics created in high temperature region of paraelectric phase of PCN.

4

Diffuse phase transition of polycrystalline (Ba0.9Sr0.1)TiO3

100%

Kajtoch C. , Gabryś M. , Bąk W. , Starzyk F.

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2010

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tom T. 62, nr 3

400-402

PL

Przedstawiono wyniki pomiarów rentgenowskich (XRD) i dielektrycznych dla polikrystalicznego (Ba0,9Sr0,1)TiO3 (BS10T). Wyniki pomiarów pokazują obecność, w temperaturze 373 K, rozmytej przemiany fazowej (DPT) pomiędzy strukturą regularną i tetragonalną. Temperatura maksimum rzeczywistej składowej przenikalności elektrycznej (ε') nie zależy od częstotliwości elektrycznego pola pomiarowego. Kąt fazowy, Φ ≈-90°, między prądem a przyłożonym napięciem elektrycznym sugeruje występowanie obszarów polarnych (klasterów) poniżej 400 K, tj. w obszarze temperaturowym DPT i w fazie paraelektrycznej.

EN

The results of X-ray diffraction (XRD) and dielectric measurements performed for polycrystalline (Ba0.9Sr0.1)TiO3 (BS10T) are presented. Data from these measurements show a presence of diffuse phase transition (DPT) between cubic and tetragonal structure at a temperature of 373 K. The temperature Tm of the maximum of real part permittivity (ε') does not depend on the frequency of the applied electric field. A phase angle, Φ ≈ -90° between current and applied voltage, suggests an occurrence of polar regions (clusters) below 400 K i.e. in the DPT temperature range of and in the paraelectric phase.

5

Evolution of electric polarization in paraelectric phase of BaTiO3

100%

Bąk W. , Kajtoch C. , Starzyk F. , Żmija J.

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2008

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tom Vol. 33, nr 2

79-82

EN

Purpose: The aim of this work has been to study electric properties of polycrystalline BaTiO3 (BT) at paraelectric phase. On the basis of the obtained results mechanism of dipolar polarization has been discussed. Design/methodology/approach: Polycrystalline samples of barium titanate were prepared using calcinations method, at the temperature about 1670 K. Dielectric measurements were carried out by means of Quatro Cryosystem 4.0 and Agilent Precision LCR meter HP4284A equipped with WinDETA 5.62 software Novocontrol. The samples were refreshed before measurements by annealing at 700 K. The dielectric measurements were carried out within the frequency range 20 Hz - 1 MHz under cooling with 2 K/min speed. Findings: The results show occurrence of maxims of dielectric permittivity (ε') and phase angle (Φ) within the "cross – over" region. The temperatures related to these maxims depend on the frequency of electric field and are higher for higher frequencies. A positive temperature coefficient (PTC) of conductivity has been found in paraelectric phase of BT. Research limitations/implications: It has been postulated, on the basis of the obtained results, that at the temperatures above 400 K (paraelectric phase) two types of polarization exist in BT: the polarization due to free dipoles (Pf) and the polarization (Pd) related to polar clusters formed by the dipoles. Originality/value: The results confirm existence of two types of polarization in paraelectric phase of BaTiO3.

6

Structure and AC conductivity of polycrystalline Pb(Cd1/3Nb2/3)O3

100%

Bąk W. , Kajtoch C. , Mroczka K. , Wójcik K.

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2008

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tom Vol. 33, nr 2

75-78

EN

Purpose: Purpose of this work was to determine crystalline structure and ac electric conductivity of polycrystalline sample Pb(Cd1/3Nb2/3)O3 (PCN) in paraelectric phase. Controversies involving uncertainties of phase transition character were the motivation of our experimental investigation: roentgenostructural, electron microscopy (SEM) and dielectric (ε') as well as electric (δ') spectroscopy. Design/methodology/approach: Polycrystalline PCN samples were prepared using hot pressing method. X-ray measurements had been performed with use of DRON3 apparatus (Cu Kα, monochromator: monocrystal LiF, at detector NaI side) with jump of 2O angle accounting for 0.02deg within a range 10-120deg. Structure images were made at room temperature with a use of electron microscope Philips SEM 525M. Dielectric measurements were made with a use of automatic measuring system Quatro Cryosystem 4.0 and Agilent Precision LCR meter HP4284A equipped with WinDETA 5.62 software Novocontrol. Before measurements, polycrystalline PCN samples were refreshed by annealing at 700 K. Next, electric measurements were carried out under cooling with 2 K/min speed. Findings: It was established that cubic phase is present within the whole range of temperatures (173 K-723 K) applied in our measurements. The polar component of the electric conductivity was dominate below the Tm temperature (Tm - temperature at which the maximal value of dielectric permittivity takes place). Above this temperature, activation energy (φ) is falling down, along increasing frequency of measuring field. Research limitations/implications: Changes of AC conductivity of PCN were interpreted in terms of polar regions properties evolution. Originality/value: Results obtained have broad the knowledge about phase transitions occurring without crystal structure change, but involving freezing of polar regions under cooling.

7

Structural and dielectric properties of polycrystalline (Ba0.9Sr0.1)TiO3

100%

Kajtoch C. , Gabryś M. , Tejchman W. , Handke B.

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2008

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tom Vol. 33, nr 2

89-92

EN

Purpose: This work is aimed to determination of the influence of Sr - ferroactive substitution on physical properties and character of phase transitions (PT) in barium titanate BaTiO3 (BT). Design/methodology/approach: Polycrystalline samples of BST-10 were prepared by means of calcination method at the 1600 K. Roentgenogram of BST-10 was made within the angles from 10 deg to 110 deg with the 0.008 deg step. Images of the morphology of the samples were taken by means of electron microscope Philips SEM 525M at room temperature. Dielectric measurements were performed with application of Quatro Cryosystem 4.0 and Agilent Precision LCR meter HP4284A equipped with WinDETA 5.62 software Novocontrol. Measurement were taken under cooling with 2 K/min speed. Measuring electric field frequency was from the range 20 Hz-1 MHz. Findings: Dielectric spectroscopy in the frequency domain was applied to measure complex dielectric permittivity and other dielectric functions of ferroelectric polycrystalline (Ba0.9Sr0.1)TiO3 (BST-10). It was established that 10% substitution of Sr in BST-10 solid solution did not change the character of the phase transitions. The temperatures of the phase transitions were correlated with low temperature of PT in SrTiO3 (ST). Similar properties of Ba and Sr ions were taken into consideration. The dipolar character of solid solution was also observed in paraelectric phase. Practical implications: Obtained results can be used to model the effects of ferroactive and nonferroactive substitutions in the A and B subnets of perovskite ferroelectrics. Originality/value: An attempt to correlate low phase angle values observed in the paraelectric phase of BTS-10 with high dielectric permittivity and the occurrence of polar regions.

8

Dielectric spectroscopy study of Ba0.98Na0.02Ti0.98Nb0.02O3 ceramic

88%

Bąk W. , Gabryś M. , Kajtoch C. , Stanuch K. , Starzyk F.

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2009

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tom Vol. 39, nr 2

107-110

EN

Purpose: The purpose of this work was to investigate dielectric properties of new ceramic solid solution Ba0.98Na0.02Ti0.98Nb0.02O3 (BNTN2) within the temperature range 153 K - 473 K. Design/methodology/approach: The dielectric spectroscopy method was applied to measure frequency and temperature dependence of complex dielectric permittivity, complex admittance, phase angle. The frequency dependence of ac conductivity at constant temperature was analysed as well as reciprocal permittivity and dielectric modulus as functions of temperature and frequency were compared. The Curie-Weiss rule and its generalized formula were applied in outcomes analysis. Findings: The ferroelectric - paraelectric (FE - PE) phase transition occurring in BNTN2 was found as having diffusive nature. In the paraelectric phase at about 400 K the diffusivity of transition step is correlated with the same kind of transition in BaTiO3 (BT) (transition of FE - PE type) and with structural transition occurring in NaNbO3 (NN). Within the temperature range below Tm = 308 K, dependences of dielectric properties of BNTN2 ceramic on temperature and frequency was found as having relaxor type of behaviour. Research limitations/implications: The confirmations of achieved findings will be possible by more precise BNTN2 structure determination by means X-ray diffraction. Also closer explanation of FE - PE phase transition can be performed by dielectric measurements within broader frequency range up to 1.8 GHz ( diffusive versus relaxor character of transition). Originality/value: The new solid solution of BNTN2 was prepared. The structure of this material was characterized as dielectrically active and having FE - PE phase transition which was described.

9

The dielectric behaviour of polycrystalline Ba0.96Na0.04Ti0.96Nb0.04O3 solid solution

88%

Bąk W. , Gabryś M. , Kajtoch C. , Tejchman W. , Starzyk F.

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2009

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tom Vol. 40, nr 1

13-16

EN

Purpose: The purpose of this work was to measure and investigate dielectric properties of new material, polycrystalline solid solution Ba0.96Na0.04Ti0.96Nb0.04O3 (BNTN4) within the temperature range 153 K-473 K. Design/methodology/approach: The dielectric spectroscopy method has been applied to measure dielectric and electric parameters within the frequencies from 20 Hz to 1 MHz. Findings: The dielectric permittivity (&epsilon') dependence on temperature (T) within the range of 473 K-225 K consist of two components: the reversly proportional one and the second one in the form of small local, transient peak at about 400 K. The global maximum is frequency dependent and above &sim 400 K along the T decrease, the dispersion of &epsilon' is initiated and low frequency dispersion of &epsilon' prevails below 250 K. Energy losses measure (&epsilon"), correlated with &epsilon'(T), is generally shifted towards lower T values. Its frequency dependence undergoes inversion which develops with T decrease and is initiated at about 370 K. The whole temperature induced phase transition turned out to be of relaxor kind and diffused process. The detailed analysis of this transition and its features was performed. Research limitations/implications: In order to determine the details of polycrystalline structure of BNTN4 new material for modelling of ferroelectric properties the precise X-ray diffraction measurements should be performed as function of T. The nature of ferroelectric - paraelectric (FE - PE) transition diffusive character will be studied by means of dielectric measurements within frequency range 1 MHz-1.8 GHz. Originality/value: The new kind of ferroelectric solid solution (BNTN4) was synthesized. The specific features of this material at low T range involves among others, the T-dependent dispersion of dielectric properties on low T side of broad &epsilon'(T) peak.

10

Dielectric properties of polycrystalline (Ba0.40Sr0.60)O3

75%

Kajtoch C. , Bąk W. , Gabryś M. , Mroczka K. , Starzyk F. , Żmija J.

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2009

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tom Vol. 40, nr 1

33-36

EN

Purpose: Purpose of this paper is to qualify of the degree and the causes of broadening of the phase transition in the polycrystalline solid solution (Ba0.40Sr0.60)TiO3 (BS60T). Design/methodology/approach: Polycrystalline samples of (Ba0.40Sr0.60)TiO3 (BS60T) were prepared by calcinations method at temperature 1570K. Images of the morphology of the samples were taken by means of electron microscope Philips SEM 525M at room temperature. Dielectric measurements were performed with application of Quatro Cryosystem 4.0 Agilent Precision LRC meter HP4824A equipped with WinDETA 5.62 software Novocontrol. Measurements were taken under cooling with 2K/min speed. Measuring electric field frequency was from the range 20 Hz - 1 MHz. Findings: The dielectrometry was applied to measure complex dielectric permittivity and other dielectric functions of ferroelectric (BS60T). It was affirmed, that 60% substitution of Sr ions changed the type of phase transition. Weak dependence of temperature Tm=208 K (temperature of maximum electric permittivity &epsilon') on frequency of the external electric field testifies about diffused character of the phase transition (DPT). The polar character of this material was also observed in the paraelectric phase (to 360 K). This observation is connected with the occurrence of polar clusters in this phase. Research limitations/implications: Results can be used in order to describe the phase transition modifications in the solid solutions with ferroactive substitutions in sublattice B of the perovskite. Originality/value: Value of this work relies on the experimental examination of the electric properties of BS60T solid solution. The low value of phase angle in the paraelectric phase is connected with the occurrence of the polar regions (clusters).