Clustering in rare-earth-doped alkaline earth fluorides (dielectric relaxation)

Andeen, Carl; Fontanella, J. J.; Wintersgill, M. C.; Welcher, None P J; Kimble, Robert J.; Matthews, G. Eric

doi:10.1088/0022-3719/14/24/012

Cited by 130 publications

(48 citation statements)

References 37 publications

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“…[1][2][3][4][5] The loss measurements were made at the five audio frequencies, 102, 12.5, 10 3 , 103.5 and 0 Hz using a fully automated, microprocessor controlled bridge constructed by one of the authors (C.G.A. )…”

Section: Ila(* Pniered)mentioning

confidence: 99%

Electrical and differential scanning calorimetry studies of poly(ethylene oxide) complexed with alkaline‐earth thiocyanates

Fontanella

Wintersgill

Calame

et al. 1985

J. Polym. Sci. Polym. Phys. Ed.

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Audio‐frequency dielectric relaxation measurements and differential scanning calorimetry studies have been performed on poly(ethylene oxide) (PEO) complexed with calcium and barium thiocyanate. The measurements were performed over the temperature range 5.5‐300 K. The relaxation spectrum for the complexed material consists of two peaks. The activation enthalpy for the peak corresponding to the γ relaxation of pure PEO depends upon the size of the dopant cation. The activation enthalpy for the second peak is independent of the nature of the dopant cation and is very similar to that observed for the αc relaxation observed in pure PEO. Furthermore, the room‐temperature electrical conductivity of the complexed materials is much smaller than that for pure PEO and hence very much less than for PEO‐complexed with alkali‐metal salts. However, above Tg the conductivity rises rapidly and is larger for the barium‐thiocyanate‐complexed PEO than for the calcium‐complexed material. Finally, the DSC studies show that one effect of the ions is to shift the glass transition to higher temperatures.

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Section: Ila(* Pniered)mentioning

confidence: 99%

Electrical and differential scanning calorimetry studies of poly(ethylene oxide) complexed with alkaline‐earth thiocyanates

Fontanella

Wintersgill

Calame

et al. 1985

J. Polym. Sci. Polym. Phys. Ed.

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“…The absolute temperature is probably accurate only to about O.1K. Other results obtained using this system are given elsewhere (19)(20)(21)(22)(23)(24).…”

Section: Methodsmentioning

confidence: 93%

Electrical relaxation in pure and alkali metal thiocyanate complexed poly(ethylene oxide)

et al. 1983

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“…The stability of type I dipoles decreases, while that of type II dipoles increases with Ar. Spectra showing up to five relaxation peaks have also been reported [2,7]. Laser-selective-excitation investigations [7] have helped to attribute the additional relaxations to F~ reorientations within polarizable clusters of two or more RE~I ions and several chargecompensating F~ ions.…”

Section: Introductionmentioning

confidence: 93%

“…The dielectric properties of alkaline-earth fluorides (MF2) doped with RE 3÷ fluorides have attracted considerable attention [1][2][3][4][5][6][7][8][9][10][11]. They have recently been reviewed by Crawford [1].…”

Section: Introductionmentioning

confidence: 99%

“…They have recently been reviewed by Crawford [1]. Andeen et al [2] Dilute solid solutions often show one or two dipole relaxations [6,8]. EPR investigations have shown that these relaxations are due to simple associates of a substitutional RE ~" ion (REM)and an interstitial fluoride ion (F~): a nearest-neighbour (nn) associate having tetragonal symmetry (type I dipole), and a next-nearest-neighbour (nnn) associate having trigonal symmetry (type II dipole) [12].…”

Section: Introductionmentioning

confidence: 99%

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Low-temperature ionic conductivity and dielectric relaxation phenomena in fluorite-type solid solutions

Wapenaar

Koekkoek

1982

Solid State Ionics

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Low-temperature ionic conductivity and dielectric relaxation phenomena in Ba 1 _xLaxF2+x crystals (1.19 X 10 -3 < x < 0.492) have been studied by ionic thermal current (ITC) and ac dielectric loss (DL) techniques. The conductivity results agree with those of an earlier ~tudy of the same crystals at higher temperatures. At low LaF 3 concentrations, i.e. 1.19 X 10 -3 ~ x ~ 2.37 X 10 -2 , the dielectric spectra show three relaxation peaks, two of which are ascribed to simple associates of interstitial F-ions (Fi) nearest-neighbour (nm) and next-nearest-neighbour (nnn) to substitutional La 3÷ ions (LaBa). They are denoted as type I and II dipoles, respectively. We attribute the third peak to angled ("L-shaped") (LaBa2~'i}' complexes. Relaxation parat~etors for the relaxations are presented. We have calculated effective dipole moments for type I . eli eli .and II dipole8 PI and/Zli , taking rote account the displacements and polarizabilities of the defects. Several combinations of host lattice cations and dQpant ions have been co~idered for the fluorites M l -xRExF2+x, i.e. M = Ca, S~Ba, and RE = La, Eu, Lu. For nearly all combinations the ratio ~[f/~ff is found to have a value of 2.4 ± 0.1. With the tt eII values thus obtained, the dipole concentrations of type I and II dipoles can be calculated. Their dependence on solute content is discussed. In the calculations, Debye-Hiickel-Lidiard interactions between defects and the charge clouds surrounding them have been taken into account. At high concentrations, i.e. 0.133 < x < 0.492, broad structureless absorption losses dominate the dielectric relaxation spectra. These losses are analysed by the fractional polarization (FP) technique, and by a special analysis of the DL data. The feasibility of these techniques is discussed. The analysis reveals that two localized relaxation processes occur in concentrated solid solutions. One is characterized by reorientation activation enthalpies (AH R) which are ghe same as the corresponding conductivity activation enthalpies (AH), and is ascr~ed to F-interstitial motion in crystal areas around defect clusters. The second process is characterized by AH R values which are much lower than AH. We propose that this process is related to F-interstitial reorientation within clusters. The results presented indicate that no typical polarizable cluster is preferred in concentrated Ba I _xLaxF2+x solid solutions.

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Clustering in rare-earth-doped alkaline earth fluorides (dielectric relaxation)

Cited by 130 publications

References 37 publications

Electrical and differential scanning calorimetry studies of poly(ethylene oxide) complexed with alkaline‐earth thiocyanates

Electrical and differential scanning calorimetry studies of poly(ethylene oxide) complexed with alkaline‐earth thiocyanates

Electrical relaxation in pure and alkali metal thiocyanate complexed poly(ethylene oxide)

Low-temperature ionic conductivity and dielectric relaxation phenomena in fluorite-type solid solutions

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