Thermodynamics of the rhombohedral-cubic phase transition of ROF with R  Y, La, Pr, Nd, SmEr

Petzel, T.; Marx, V.; Hörmann, Bernadette

doi:10.1016/0925-8388(93)90466-z

Cited by 40 publications

(24 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This structure can also be described in the hexagonal setting with the unit cell containing six formula units ( a =0.4057 nm and c =2.0211 nm). The lattice parameters obtained in this study are compared in Table I with values from the literature 1,7,10,11 . There is good agreement except for the data of Tyagi 11 .…”

Section: Resultssupporting

confidence: 65%

Lanthanum Oxyfluoride: Structure, Stability, and Ionic Conductivity

Jacob

Saji

Waseda

2006

Int J Applied Ceramic Tech

View full text Add to dashboard Cite

Structure and phase transition of LaO1−xF1+2x, prepared by solid‐state reaction of La2O3 and LaF3, was investigated by X‐ray powder diffraction and differential scanning calorimetry for both positive and negative values of the nonstoichiometric parameter x. The electrical conductivity was investigated as a function of temperature and oxygen partial pressure using AC impedance spectroscopy. Fluoride ion was identified as the migrating species in LaOF by coulometric titration and transport number determined by Tubandt technique and EMF measurements. Activation energy for conduction in LaOF was 58.5 (±0.8) kJ/mol. Conductivity increased with increasing fluorine concentration in the oxyfluoride phase, suggesting that interstitial fluoride ions are more mobile than vacancies. Although the values of ionic conductivity of cubic LaOF are lower, the oxygen partial pressure range for predominantly ionic conduction is larger than that for the commonly used stabilized‐zirconia electrolytes. Thermodynamic analysis shows that the oxyfluoride is stable in atmospheres containing diatomic oxygen. However, the oxyfluoride phase can degrade with time at high temperatures in atmospheres containing water vapor, because of the higher stability of HF compared with H2O.

show abstract

Section: Resultssupporting

confidence: 65%

Lanthanum Oxyfluoride: Structure, Stability, and Ionic Conductivity

Jacob

Saji

Waseda

2006

Int J Applied Ceramic Tech

View full text Add to dashboard Cite

show abstract

“…EDX-measurements on oxide fluorides of the stoichiometric composition ROF with R = Sm, Eu, Gd, Dy and Er, which are a well characterized group of compounds [1], were performed in order to test the transferability of the calibration with YbO1+XFt -2X. The different positions of the three rare earth element Fig.…”

Section: Stoichiometric Oxide Fluorides Of Sm Eu Gd Dy and Ermentioning

confidence: 99%

“…10 µm. Since the rare earth oxide fluorides of composition ROF can be considered as stoichiometric [1], all samples with x = 0 consisted of grains of identical composition. In cases where x > 0 the samples were inhomogeneous and consisted of grains of measurably different compositions.…”

Section: Sample Preparation and Characterizationmentioning

confidence: 99%

Quantitative determination of F:O ratios in rare earth oxide fluorides by energy dispersive X-ray analysis

Marx

Greis

Strübig

et al. 1996

Fresenius J Anal Chem

Self Cite

View full text Add to dashboard Cite

show abstract

“…This change is a first-order transition, and it is normally not possible to preserve the cubic symmetry by quenching. The mechanism behind the structure transformation is not known, but it is possibly related to an order-disorder reaction among the anions (Petzel et al 1993, Müller & Petzel 1995, Fergus 1996, Achary et al 1998.…”

Section: Introductionmentioning

confidence: 97%

HALENIUSITE-(La) FROM THE BASTNAS DEPOSIT, VASTMANLAND, SWEDEN: A NEW REE OXYFLUORIDE MINERAL SPECIES

Holtstam¹,

Grîns²,

Nysten³

2004

The Canadian Mineralogist

View full text Add to dashboard Cite

Håleniusite-(La), a new mineral species whose ideal formula is (La,Ce)OF, is cubic and has a unit-cell parameter a equal to 5.6282(5) Å, V = 178.28(5) Å 3 , for Z = 4. The strongest five lines in the X-ray powder-diffraction pattern obtained with a GuinierHägg camera [d in Å (I obs )(hkl)] are: 3.25(100)(111), 2.815(31)(200), 1.991(61)(220), 1.697(46)(311) and 1.292(15)(331). The crystal structure was refined in space group Fm3m from powder data using the Rietveld method, to an R F value of 5.1%. The mineral is shown to be isostructural with fluorite, and the average metal-anion distance is 2.437(1) Å for håleniusite-(La). D(calc.) ≈ 6.5 g/cm 3 . The atomic ratio La/(La + Ce) is 0.506 -0.001 (range 0.485-0.528). Håleniusite-(La) is powdery, with a distinct yellow color. It is associated with bastnäsite-(La), brochantite, ferriallanite-(Ce) and quartz in the type specimen, and was found on the dumps of the Bastnäs Cu-REE mines in Västmanland, Sweden. Additional specimens from the same locality contain cerite-(Ce), molybdenite and amphibole. Håleniusite-(La) is a secondary mineral, formed by alteration of primary bastnäsite-(La), most likely via a decarbonation reaction, (La, Ce)CO 3 F → (La, Ce)OF + CO 2 . The name of this new mineral honors Ulf Hålenius, Professor of Mineralogy at the Swedish Museum of Natural History. SOMMAIRELa håléniusite-(La), nouvelle espèce minérale dont la formule idéale est (La,Ce)OF, a une symétrie cubique et un paramètre réticulaire a égal à 5.6282(5) Å, V = 178.28(5) Å 3 , pour Z = 4. Les cinq raies les plus intenses du spectre de diffraction X, méthode des poudres, tel qu'obtenu avec une chambre Guinier-Hägg [d en Å (I obs )(hkl)], sont: 3.25(100)(111), 2.815(31)(200), 1.991(61)(220), 1.697(46)(311) et 1.292(15)(331). La structure cristalline a été affinée dans le groupe spatial Fm3m avec la méthode de Rietveld, jusqu'à une valeur R F de 5.1%. Le minéral possède la structure de la fluorite, et la distance moyenne de métal à anion est 2.437(1) Å. La densité calculée est égale à 6.5 g/cm 3 . Le rapport La/(La + Ce) est 0.506 -0.001, et varie entre 0.485 et 0.528. La håléniusite-(La) est pulvérulente et de couleur jaune. Elle est associée à la bastnäsite-(La), brochantite, ferriallanite-(Ce) et quartz dans l'échantillon-type. Nous l'avons découverte dans des haldes de mines désaffectées de cuivre et de terres rares à Bastnäs, Västmanland, en Suède. Des échantillons additionnels du même endroit contiennent cérite-(Ce), molybdénite et une amphibole. La håléniusite-(La), d'origine secondaire, s'est formée par altération de la bastnäsite-(La) primaire, tout probablement par une réaction de décarbonatation, (La, Ce)CO 3 F → (La, Ce)OF + CO 2 . Le nom choisi honore Ulf Hålenius, Professeur de Minéralogie au Musée d'Histoire Naturelle de Suède.(Traduit par la Rédaction)

show abstract

Thermodynamics of the rhombohedral-cubic phase transition of ROF with R  Y, La, Pr, Nd, SmEr

Cited by 40 publications

References 9 publications

Lanthanum Oxyfluoride: Structure, Stability, and Ionic Conductivity

Lanthanum Oxyfluoride: Structure, Stability, and Ionic Conductivity

Quantitative determination of F:O ratios in rare earth oxide fluorides by energy dispersive X-ray analysis

HALENIUSITE-(La) FROM THE BASTNAS DEPOSIT, VASTMANLAND, SWEDEN: A NEW REE OXYFLUORIDE MINERAL SPECIES

Contact Info

Product

Resources

About