Behaviour of thermo-E.M.F. of cerium under hydrostatic pressure up to 75 kbars

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HAL Id: jpa-00218924

https://hal.archives-ouvertes.fr/jpa-00218924

Submitted on 1 Jan 1979

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

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Behaviour of thermo-E.M.F. of cerium under hydrostatic pressure up to 75 kbars

L. Khvostantsev, N. Nickolaev

To cite this version:

L. Khvostantsev, N. Nickolaev. Behaviour of thermo-E.M.F. of cerium under hydrostatic pres- sure up to 75 kbars. Journal de Physique Colloques, 1979, 40 (C5), pp.C5-383-C5-384.

�10.1051/jphyscol:19795138�. �jpa-00218924�

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JOURNAL DE PHYSIQUE

Colloque C5, supplement au n° 5, Tome 40, Mai 1979, page C5-383

Behaviour of thermo-E.M.F. of cerium under hydrostatic pressure up to 75 kbars

L. G. Khvostantsev and N. A. Nickolaev

Institute of High Pressure Physics, Academy of Sciences of the U.S.S.R.

142092 Troitsk, Moscow region, U.S.S.R.

Résumé. — Un appareil de type toroïdal est utilisé pour l'obtention des pressions. Le pouvoir thermoélectrique du cérium demeure positif. Un domaine de transition existe entre la phase a et 7 entre 7,5 et 10 kbar après la transition électronique à 7,5 kbar et entre la phase a et a' entre 52 et 72 kbar à la température ambiante. Le pouvoir thermoélectrique augmente au moment de la transition a -• a' pour atteindre une valeur du même ordre de grandeur que celui de la phase y.

Abstract. — The apparatus of toroid type was used for pressure obtaining. Thermo-e.m.f. of cerium does not change the positive sign. Transitional domain of pressure exists between y-phase and real a-phase (7.5-10 kbar) after electronic transition at 7.5 kbar and between a-phase and real a'-phase (52-72 kbar) of cerium at normal temperature. Thermo-e.m.f. increases at a -» a' transition and thermo-e.m.f. of a'-phase has great magnitude like the initial thermo-e.m.f. of y-phase of cerium.

1. Experiment and results. — An apparatus of type toroidwas used [1] for generation of high pressure.

Teflon ampoule with useful volume of 1.8 cm

³

and copper covers was filled by silicon liquid or pure petrol which solidify about 20 kbar and 40 kbar accordingly at room temperature. The pressure was measured by manganine gauge and jumps of bismuth at 25.5 kbar and 74 kbar. The sample of cerium (height 16 mm and cross section 2 x 2 mm

2

) of purity 99.93 % was mounted on the lower cover to make thermal contact with this cover and matrice of apparatus toroid and thus stabilise the temperature of lower end of sample during experiment. Copper- constantan thermocouples were welded to sample.

Thermo-e.m.f. was measured at two-three temperature gradient along the sample at each point of pressure.

This gave possibility to determine correct differential thermo-e.m.f. and its dependence on temperature near room temperature.

The magnitude of S

^Ce

of y-phase (figure 1) increases considerably with pressure and velocity of its increas- ing grows with pressure. S

C(

. has great magnitude (10.4 uV/K) among the magnitude of the thermo- power of ordinary metals and reaches 19 uV/K at 8 kbar.

At 8.1 kbar and temperature 303 K the magnitude of S

Ce

drops sharply and has yet great changing with increasing pressure above this point of pressure on some kbars. And then S

Ce

of a-phase goes smoothly to minimum of its magnitude (2 uV/K) at 23 kbar.

Above this point of pressure 5

C e

increases its magni- tude slowly u p to 4 (xV/K at 52 kbar.

At 52 kbar S

^Ce

(P) has distinct knick and between 52 kbar and 74 kbar increases from 4 uV/K to 10 uV/K.

Fig. 1. — The absolute thermoelectric power versus pressure for Ce sample.

In the y-phase region (dS

c

JdT)

p

is negative and in the a-phase it changes sign [2]. According to our data (dS

^c

JdT)

^P

of a-phase has positive sign only up to 23 kbar and above 23 kbar its sign becomes negative. Thus, absolute thermo-e.m.f. has negative temperature coefficient for all part of thermo-e.m.f.

dependence on pressure where thermo-e.m.f. is increasing with pressure.

2. Discussion. — Firstly, there is possibility to draw the picture of nature of y -> a transition of cerium.

Initially, in accordance with equilibrium line at the point of P-Jdiagram (P — 7.6-8 kbar and ambient temperature), 4f-electrons begin to populate critically Fermi level. This situation leads to electronic tran-

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19795138

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C5-384 L. G. KHVOSTANTSEV AND N. A. NICKOLAEV

sition of cerium and leads to qualitative changing electron and phonon spectrum. This state of cerium was displayed as sharp drops of dependence on pressure of electroresistance, thermo-e.m.f., galvano- magnetic characteristic and velocity of propagation of ultrasonic waves on cerium. But the curves of thermal analysis AT(P) and relative change of volume AV/Vo(P) have knick only at this pressure [3]. The maximum on the dependence AT(P) exists at 8.5 kbar and connects with the most velocity of relative change of volume on the dependence AV/Vo(P). Thermal effect and anomalous great relative change of volume of cerium finish about 10 kbar. The magnitudes of electrd-resistance, thermo-e.m.f., galvanomagnetic characteristic and ultrasonic data change considerably yet on this range of pressure from 7.6 kbar to about 10 kbar.

Thus, the range of pressure from 7.5 kbar to 10 kbar is transition range from y-phase to cc-phase at ambient

temperature and real a-phase with its inherent regular dependence on the pressure of electrical, elastic, thermal and volumetric characteristics begin to exist above - ^{10 kbar.}

Contrary to [2] thermo-e.m.f. increases slowly above 23 kbar. Influence of 4f-level on the physical properties of cerium begin to diminish above 23 kbar.

So significant increasing of thermo-e.m.f. during a

+

a' phase transition and great positive magnitude of thermo-e.m.f. of a'-phase of cerium may be connect with disappearing of 4f-level contribution to density of states on the Fermi level. This fact give possibility to suggest that the stability of a-phase causes by contribution of a 6s5d4f-hybridization to binding energy of structure of a-phase.

Pressure extending of

y +

cc phase transition of cerium is conditioned by physical phenomena in contrast with phase transition in SmS [4]. We think such situation take place for cc

+

a' transition also.

References

[ I ] KHVOSTANTSEV, L. G., VERESHCHAGIN, L. F., NOVIKOV, A. P., Device of Toroid Type for High Pressure Generation (to be published in High Temp.-High Press.).

[2] RAMESH, T. G., RESHAMWALA, A. S. and RAMASECHAN, S., Pramina 2 (1974) 171, Solid State Commun. 15 (1974) 1851.

[3] LEGER, I. M., BASTIDE, I. P., MASSAT, H., SCHAUFELBER, P. H., High Temp.-High Press. 17 (1975) 351.

[4] APTEKAR, I. A. et al., Fiz. Tverd. Tela 19 (1977) 3180.

Behaviour of thermo-E.M.F. of cerium under hydrostatic pressure up to 75 kbars

HAL Id: jpa-00218924

https://hal.archives-ouvertes.fr/jpa-00218924

Submitted on 1 Jan 1979

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Behaviour of thermo-E.M.F. of cerium under hydrostatic pressure up to 75 kbars

L. Khvostantsev, N. Nickolaev

To cite this version:

L. Khvostantsev, N. Nickolaev. Behaviour of thermo-E.M.F. of cerium under hydrostatic pres- sure up to 75 kbars. Journal de Physique Colloques, 1979, 40 (C5), pp.C5-383-C5-384.

�10.1051/jphyscol:19795138�. �jpa-00218924�

Colloque C5, supplement au n° 5, Tome 40, Mai 1979, page C5-383

Behaviour of thermo-E.M.F. of cerium under hydrostatic pressure up to 75 kbars

L. G. Khvostantsev and N. A. Nickolaev

Institute of High Pressure Physics, Academy of Sciences of the U.S.S.R.

142092 Troitsk, Moscow region, U.S.S.R.

1. Experiment and results. — An apparatus of type toroidwas used [1] for generation of high pressure.

Teflon ampoule with useful volume of 1.8 cm

and copper covers was filled by silicon liquid or pure petrol which solidify about 20 kbar and 40 kbar accordingly at room temperature. The pressure was measured by manganine gauge and jumps of bismuth at 25.5 kbar and 74 kbar. The sample of cerium (height 16 mm and cross section 2 x 2 mm

) of purity 99.93 % was mounted on the lower cover to make thermal contact with this cover and matrice of apparatus toroid and thus stabilise the temperature of lower end of sample during experiment. Copper- constantan thermocouples were welded to sample.

Thermo-e.m.f. was measured at two-three temperature gradient along the sample at each point of pressure.

This gave possibility to determine correct differential thermo-e.m.f. and its dependence on temperature near room temperature.

The magnitude of S

of y-phase (figure 1) increases considerably with pressure and velocity of its increas- ing grows with pressure. S

. has great magnitude (10.4 uV/K) among the magnitude of the thermo- power of ordinary metals and reaches 19 uV/K at 8 kbar.

At 8.1 kbar and temperature 303 K the magnitude of S

drops sharply and has yet great changing with increasing pressure above this point of pressure on some kbars. And then S

of a-phase goes smoothly to minimum of its magnitude (2 uV/K) at 23 kbar.

Above this point of pressure 5

increases its magni- tude slowly u p to 4 (xV/K at 52 kbar.

At 52 kbar S

(P) has distinct knick and between 52 kbar and 74 kbar increases from 4 uV/K to 10 uV/K.

Fig. 1. — The absolute thermoelectric power versus pressure for Ce sample.

In the y-phase region (dS

JdT)

is negative and in the a-phase it changes sign [2]. According to our data (dS

JdT)

of a-phase has positive sign only up to 23 kbar and above 23 kbar its sign becomes negative. Thus, absolute thermo-e.m.f. has negative temperature coefficient for all part of thermo-e.m.f.

dependence on pressure where thermo-e.m.f. is increasing with pressure.

2. Discussion. — Firstly, there is possibility to draw the picture of nature of y -> a transition of cerium.

Initially, in accordance with equilibrium line at the point of P-Jdiagram (P — 7.6-8 kbar and ambient temperature), 4f-electrons begin to populate critically Fermi level. This situation leads to electronic tran-

Thus, the range of pressure from 7.5 kbar to 10 kbar is transition range from y-phase to cc-phase at ambient

temperature and real a-phase with its inherent regular dependence on the pressure of electrical, elastic, thermal and volumetric characteristics begin to exist above - 10 kbar.

Contrary to [2] thermo-e.m.f. increases slowly above 23 kbar. Influence of 4f-level on the physical properties of cerium begin to diminish above 23 kbar.

So significant increasing of thermo-e.m.f. during a

Pressure extending of

cc phase transition of cerium is conditioned by physical phenomena in contrast with phase transition in SmS [4]. We think such situation take place for cc

a' transition also.

temperature and real a-phase with its inherent regular dependence on the pressure of electrical, elastic, thermal and volumetric characteristics begin to exist above - ^{10 kbar.}