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1

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

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

Archives of Materials Science and Engineering

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2008

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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.

2

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

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

Archives of Materials Science and Engineering

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2008

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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.

3

Relaxor properties of Ba1-xNaxTi1-xNbxO3 at low temperatures

Bąk W.

Archives of Materials Science and Engineering

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2008

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Vol. 34, nr 1

23-26

EN

Purpose: The purpose of this paper is to investigate ferroelectric relaxor behavior of polycrystalline solid solutions of Ba1-xNaxTi1-xNbxO3 (for x = 0.3 and x = 0.4) at low temperatures (113 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: Temperature dependences of real (ε') and imaginary (ε'') parts of dielectric permittivity confirm relaxor type of polarization behavior for both investigated materials. Experimental findings are in good agreement with data published in literature. Diffused phase transition of relaxor character is analysed in the terms of departure from Curie-Weiss rule. A dependence of the temperature related to the maximum of dielectric permittivity on the frequency has activated character. Different thermal activation energies found for the investigated materials may be related to their different microstructures. Research limitations/implications: Further investigations should be carried on in a broaden frequency range (up to 1.8 GHz) in order to establish an influence of network dynamics on ferroelectric-paraelectric phase transition. Originality/value: Relaxor behaviour in polycrystalline solid solution of Ba1-xNaxTi1-xNbxO3 (for x = 0.3 and x = 0.4) is described.

4

Elevated temperature induced dispersion phenomena in Ba1-xNaxTi1-xNbxO3

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

Archives of Materials Science and Engineering

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2008

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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.