Effect of a DC bias field on the ferroelectric phase transition of KTN

Toulouse, J.; Wang, X. M.

doi:10.1080/00150199008214592

Cited by 4 publications

(3 citation statements)

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“…Figure 2b shows CL data for the 5% Nb-melt material in which the 12 keV curve has an intensity step during heating near 63 K. The equivalent step temperature is displaced to ~80 K for the 6 keV measurements. Temperature variations for phase transitions in KTN exist from electric field effects [19,20]. The changes for CL data are consistent with effects from surface charging [22], as the electron ranges are <1 µm, while surface potentials may be a few volts (i.e.…”

Section: Methodssupporting

confidence: 65%

“…The 6 keV intensity changes resemble the intensity spikes seen with KNbO 3 . Surface relaxations and temperature movements of the transition temperatures may in part relate to the physical geometry, dislocation density, impurities and compaction differences between the surface and bulk but, certainly for KTN, it may be emphasised by electric field effects which also induce changes in transition temperature [19,20].…”

Section: Results and Commentsmentioning

confidence: 99%

“…KTN phase transitions have shown hysteresis effects and are sensitive to electric fields which can raise or lower the transition temperatures [19,20] by ~1 degree per kV/cm (for fields of <10 kV/cm).…”

Section: Introductionmentioning

confidence: 99%

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Cathodoluminescence from mixed KTaO₃‐KNbO₃ crystals

Kibar

Townsend

Wang

et al. 2007

Phys. Status Solidi (c)

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Cathodoluminescence spectra are shown for a sequence of mixed crystals of KTaO 3 :KNbO 3 . The luminescence emission bands are broadly similar across the spectrum from 250 to 850 nm, although their relative strengths are sensitive to composition and temperature. A UV band near 330 nm is only well resolved in some compositions and a broad line near 700 nm may arise from Cr ions. The presence of low temperature phase transitions within the crystals is evidenced by intensity steps and spectral changes of the cathodoluminescence. Hysteresis is seen, as are domain effects and electric field shifts of the transition temperatures. The cathodoluminescence of the surface material reveals more transitions than are reported from earlier bulk studies. ] pre-phase softening, precursor effects, plus additional phases [4,7] and existence of dipolar glassy states [8]. In part some differences may result from inaccuracies in the measurement of the Nb concentration, since there are significant differences between compositions of the growth melt and the crystal, as well as sample uniformity.The KTN materials offer a useful framework to explore phase transitions by variations in optical properties. Optical absorption and second harmonic generation have also revealed extra sub-phases [7]. Luminescence properties similarly reveal phase transitions, as briefly reviewed [9], with changes in spectra between phases (as for NH 4 Br [10]), minor wavelength shifts [11], charge release and intense emission events at the phase transition for KNbO 3 [12], irreversible phase changes [13], or those which require a high temperature regeneration of the starting phase [14] and hysteresis effects between cooling and heating [12]. There can be differences between the spectra and the number of detectable phase transitions when recording luminescence with X-ray excitation (RL, radioluminescence) or electrons (CL, cathodoluminescence) [15]. Such differences exist since surface relaxation processes sensed by CL can proceed more readily than those in the bulk material, as for RL. Surface damage as the result of polishing and/or contaminants may additionally result in local changes in phase, composition or dislocation density. Unexpected events can occur with dramatic intensity steps during heating or cooling at temperatures

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Section: Methodssupporting

confidence: 65%

Section: Results and Commentsmentioning

confidence: 99%