A comparative study of La3+Fi− complexes in threeMF2 fluoride crystals

Ong, S.H.; Jacobs, P. W. M.

doi:10.1016/0022-4596(80)90567-8

Cited by 36 publications

(15 citation statements)

References 19 publications

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“…A more convincing argument for the proposed attribution, also pointed out by Ong and Jacobs [3], is found in the similarity between the activation enthalpy for the reorientation of type II dipoles in BaF 2 : La 3+, and that for the only relaxation observed in the TSP spectrum of BaF 2 :Tb 3+ [18]. Since the ionic radii of Tb 3+ and Gd 3+ are almost the same, it is no doubt correct to attribute this relaxation to nnn associates.…”

Section: Z Simple Associatesmentioning

confidence: 72%

“…ITC spectra of Ba 1 _xLaxF2+x solid solutions containing low and moderate dopant concentrations (10 -4 <x < 10 -2) show peaks corresponding to type I and II dipoles, and a small third peak ascribed to oxygen in the lattice [3,4]. At high concentrations of dopant, up to x = 0.26, the spectra are dominated by a high fourth peak due to the relaxation of macroscopic space charges [5].…”

Section: Ked Icapenaar Et Al/low-ternperature Ionic Conductivitymentioning

confidence: 98%

“…1). Ong and Jacobs [3] have pointed out that the attribution of the higher relaxation peak (type II) to nnn associates is substantiated by the EPR spectra of BaF 2 : Gd 3+ [27,28] and BaF 2 : Yb 3+ [29], which are dominated by a trigonal spectrum. However, lattice simulation calculations [13] have shown that the results for BaF 2 : Gd 3+ and BaF 2 : Yb 3+ cannot be extended to BaF 2 : La 3+.…”

Section: Z Simple Associatesmentioning

confidence: 99%

“…In this section we discuss the type I and type II dipoles, which have been identified [3,4] as simple nn and nnn associates of La~a and F~ defects, respectively ( fig. 1).…”

Section: Z Simple Associatesmentioning

confidence: 99%

“…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%

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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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Section: Z Simple Associatesmentioning

confidence: 72%

Section: Ked Icapenaar Et Al/low-ternperature Ionic Conductivitymentioning

confidence: 98%

Section: Z Simple Associatesmentioning

confidence: 99%

“…In this section we discuss the type I and type II dipoles, which have been identified [3,4] as simple nn and nnn associates of La~a and F~ defects, respectively ( fig. 1).…”

Section: Z Simple Associatesmentioning

confidence: 99%