Kinetics of the dhcp-fcc phase transformation in La under pressure

Merkau, B.; Holzapfel, W. B.

doi:10.1016/0378-4363(86)90569-3

Cited by 6 publications

(8 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The phase transition fee-• rf-fcc is believed to be of second order [6,7,25]. For second-order phase transitions there is no latent heat and no change of density at the phase transition and the slope of the phase [24]; phase boundary fcc-^-fcc (solid line) from [25] (resistance measurements) and [7] (x-ray diffraction); •, this work. boundary dpidT is given by the Ehrenfest relations dp _^ ^Cp _ Aa dT TVAa AK '…”

Section: Novel Reentrant High Pressure Phase Transition In Lanthanummentioning

confidence: 98%

Novel reentrant high pressure phase transtion in lanthanum

Porsch

Holzapfel

1993

Phys. Rev. Lett.

View full text Add to dashboard Cite

High presure x-ray diffraction experiments with synchrotron radiation in an extended pressure range up to 67 GPa reveal a novel phase transition of La: At about 60 GPa the low pressure fee structure of La is recovered from the distorted fee (^-fcc) phase. The reappearance of the high symmetry cubic structure at higher pressure implies that the ^-fcc phase, which also appears in other lanthanides, is not a precursor of the low symmetry structures caused by the so-called /delocalization. A possible mechanism for the reentrant behavior is considered and the phase diagram of La is discussed. PACS numbers: 62.50.-l-p, 64.70.Kb Under pressure the regular trivalent lanthanide elements show a well-known series of close packed structures [1]hep-> Sm-type-• dhcp-> fee .The same sequence is shown by these elements at ambient conditions with decreasing atomic number. According to band structure calculations [2][3][4], the structural stability of these lanthanide metals is controlled by the d occupation number which decreases with increasing atomic number and increases under pressure due to s~-*d transfer.Systematic high pressure x-ray diffraction studies in wider pressure ranges [5][6][7][8] have revealed one more common structure for the regular lanthanides beyond the fee phase for the elements La, Pr, Nd, Pm, Sm, Gd, Tb, and Dy. This additional structure has been designated as "distorted fee" (d-fcc) because there are additional superstructure reflections in the fee diffraction pattern. Though there are many proposals for the structure of the d-fcc phase [3,[9][10][11], final agreement has not been obtained. A separate paper is devoted to this question [12].At still higher pressures the early lanthanides following Ce become 'irregular" and form structures of low symmetry [7]. The occurrence of these phases of low symmetry is attributed to the delocalization of 4/electrons [13]. However, La has no localized / electrons at ambient conditions. If La remains an sd band transition metal up to ultrahigh pressure [14], such structures should not appear in La at high pressure. This question has stimulated the present study.Energy dispersive x-ray diffraction with synchrotron radiation at HASYLAB (DESY) was used to study the structural behavior of La under pressure up to 67 GPa. The experimental setup with diamond anvil cell and ruby manometer has been described previously [15]. The nonlinear pressure scale [16] was used for the ruby manometer and mineral oil was used as the pressure transmitting medium. The chemical analysis of the La material provided by Gschneidner is given elsewhere [7].The two phase transitions of La at 2.5 GPa from dhcp to fee and at 7 GPa to d-fcc are well known [6]. It was noticed also previously [6] that the intensity of the superstructure reflections of the d-fcc phase increase continuously with increasing pressure. At 26 GPa the superstructure reflections (101), (105), and (113) are well developed (Fig. 1). However, the present study shows that the intensity of these superstructure reflections decreases ...

show abstract

Section: Novel Reentrant High Pressure Phase Transition In Lanthanummentioning

confidence: 98%

Novel reentrant high pressure phase transtion in lanthanum

Porsch

Holzapfel

1993

Phys. Rev. Lett.

View full text Add to dashboard Cite

show abstract

“…Comparing the peak intensities of both the phases, the transformation degree x(t) (the amount of high pressure phase) as a function of time can be obtained. This method has been successfully applied to study of kinetics of pressure induced phase transitions in PbO 2 (Dachlli and Roy 1961), KCl (Hamaya and Akimoto 1981), GeO 2 (Zeto and Roy 1969;Brar and Scloessin 1981), Fe 2 O 3 (Goto 1964), RbI (Hamaya et al 1986), La (Merkau and Holzapfel 1986;Kruger et al 1990) and other compounds.…”

Section: Experimental Reviewmentioning

confidence: 99%

“…Kinetics of structural phase transitions have been investigated for various solids in a DAC (Brar and Scloessin 1981;Merkau and Holzapfel 1986;Kruger et al 1990) as well as in other high pressure devices (Hamaya and Akimoto 1981;Hamaya et al 1986). The essential problems of the diffraction methods lie in the interpretation of the measured transformation degree x(t) and its fit to the Avrami equation without knowing further characteristics quantities like nucleation rates or growth velocities.…”

Section: Kinetics Of Phase Transition In a Diamond Anvil Cell (Dac)mentioning

confidence: 99%

“…Much faster transition kinetics are observed if a solid pressure transmitting medium is Table 6. Comparison of parameters n and k for α-quartz → rutile transformation in GeO 2 between Merkau and Holzapfel (1986) and Kruger et al (1990).…”

Section: Bi(i)-(ii)mentioning

confidence: 99%

“…The study of phase transformation kinetics yields data on the reaction velocity and additional information on the basic mechanisms of the transition. This allows a more accurate extrapolation of the phase equilibria to low tem-peratures (Merkau and Holzapfel 1986;Jeanloz 1987;Kruger et al 1990) and the comparison with theoretical results. In addition, the kinetics of phase changes under pressure is of basic importance for understanding the physical and chemical reactions that control the formation of high-pressure phases with special properties.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Kinetics of pressure induced structural phase transitions—A review

Shekar

Rajan

2001

Bull Mater Sci

View full text Add to dashboard Cite

The current status of experimental as well as theoretical advances in the understanding of kinetics of structural phase transitions is reviewed. A brief outline of the classification of phase transitions and classical ideas in the theory of kinetics of phase change is presented first. High pressure experimental techniques developed for studying the kinetics of structural transitions are reviewed and the salient features of each technique is brought out. The experimental technique using the diamond anvil cell (DAC) and image processing gets special mention as it promises to impart a new direction to this field. The usefulness of kinetic parameters in understanding the mechanism of a phase transition is examined. Typical examples from the literature are provided to give a flavour for these kind of studies. In conclusion, several open questions are raised which could pave way for future work in this area.

show abstract

Specific heat ofd-hcp and fcc lanthanum under high pressure

Bohn

Eichler

1991

Z. Physik B - Condensed Matter

View full text Add to dashboard Cite

Kinetics of the dhcp-fcc phase transformation in La under pressure

Cited by 6 publications

References 6 publications

Novel reentrant high pressure phase transtion in lanthanum

Novel reentrant high pressure phase transtion in lanthanum

Kinetics of pressure induced structural phase transitions—A review

Specific heat ofd-hcp and fcc lanthanum under high pressure

Contact Info

Product

Resources

About