OBSERVATION OF SUCCESSIVE PHASE TRANSITIONS IN SnTe SINGLE CRYSTALS

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OBSERVATION OF SUCCESSIVE PHASE TRANSITIONS IN SnTe SINGLE CRYSTALS

I. Ortalli, G. Fedeli, K. Kobayashi, K. Komatsubara

To cite this version:

I. Ortalli, G. Fedeli, K. Kobayashi, K. Komatsubara. OBSERVATION OF SUCCESSIVE PHASE

TRANSITIONS IN SnTe SINGLE CRYSTALS. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-

596-C2-567. �10.1051/jphyscol:19792208�. �jpa-00218587�

JOURNAL DE PHYSIQUE

Colloque C2, supplkment au n o 3, Tome 40, mars 1979, page C2-596

OBSERVATION OF SUCCESSIVE PHASE TRANSITIONS I N S n T e SINGLE CRYSTALS I. Ortalli, G. Fedeli, K.L.I. ~oba~ashi' and K.F. ~omatsubara*

Physics I n s t i t u t e , U n i v e r s i t y o f Ferrara

a d

Pamna, C.N.S.M.-Pma, I t a Z y

X

Central Research Laboratory, Hitachi Ltd. Kokubunji, Tokyo

185,

Japmz

RBsum6.- Nous avons observe une transition de phase prss de 22 K dans un 6chantillon de SnTe avec deux techniques differentes : la

spectroscopic

de Msssbauer et la resistivitb Slectrique. Les me- sures Msssbauer rdvslent une variation de la fraction d'effet sans recul en fonction de la tempb- rature.

On

observe de m8me une anomalie dans la variation de la resistivitB Blectrique.

Abstract.- A phase transition at 22 K was observed in p-type single crystal of SnTe by assbauer spectroscopy and electrical resistivity. At this temperature the recoilless fraction versus tem- perature curve shows a dip and the resistivity also shows a slight jump at the same temperature.

This displacive phase transition in SnTe has been studied by many workers by different experimen- tal methods 11-81.

Recently 161 it was found that the assbauer measurements in SnTe (p = 2.0 x

lo2'

~ m - ~ ) polycrys-

tals show a structural phase transition near 160 K and a successive phase transition at about 20 K. The latter is ascribed to antiferroelectric phase tran- sition. The explanation was that in SnTe there is lattice mode at the BZ boundary whose frequency approaches zero at the latter transition temperatu- re.

An anomalous increase of the electrical re- sistivity at 89 K in SnTe (p = 1.80 x

loz0

~ m - ~ ) has been observed by Kobayashi et al. 151. They have tried to explain their data by assuming a softening of carrier dependent transverse optical phonon. Ka- tayama /9/ has calculated the mechanisms due to the softening of the transverse optical (TO) phonon in- teracting with conduction carriers in two bands.

The difference in the transition type and the transition temperatures can be explained by assuming that the TO mode, due to the phonon inte- raction, depends on the concentration of the car- riers in agreement with Iizumi 141 and Sugai et al.

1101.

They suggest that the ferroelectric phase transition temperature decreases with increasing carrier concentration.

For these reasons two of us (1.0. and K.L.I.K.) planned to analyse the same single crys-

tal of SnT.e with two different techniques. The sam- ple for Msssbauer spectroscopy was prepared from a solution grown single crystal of SnTe with hole concentration of 1.8 x

lo2'

cm-3 at

77

K. Electri- cal resistivity was also measured in a sample

prepared from a crystal in the same lot from which the assbauer sample was prepared. The area for the

~Gssbauer spectroscopy was about 9 mm2 and the ex- perimental procedure was described elsewhere in 161.

In the figure the area (proportional to recoil- less fraction f ) is plotted as a function of tempe- rature.

a a

^1.9

t

-

³⁰

1.7

1.3 1 . ' . 1 . 1 2 0

0 10 2 0 30 4 0

TEMPERATURE (K)

Fig. 1 : Experimental data of the Mijssbauer area and resistivity measurements temperature.

The solid line represents the theoretical tempera- ture dependence of f on the basis of Debye approxi- mation using MEssbauer temperature B M o f 150 K (the value calculated from the slope in the range 66 % 47 K). The sharp V-shape dip is clearly seen at about 22 K. Electrical resistivity measurements show a slight jump just at the temperature where V-shape anomaly is observed, i.e. 22

K,

as shown in the figure.

The explanation of the latter results is not very simple.

In fact the resistivity

-

temperature curve/5/,

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792208

the neutron spectroscopy /4/ and heat capacity /7/

measurements show an anomaly at 89 K in a sample prepared by Hitachi Laboratory with the same concen- tration of conduction carriers. This anomaly was well interpreted as a result of TO phonon softening accompanying the 2nd order cubic - rhombohedra1

(c' 3v

)

phase transition. Usually it is considered that the anomalous mode is originated from

a

softe- ning of the TO mode at the center of BZ. The phase transition, found by different groups at 89 K, can be explained by assuming that the TO mode, caused by the TO phonon interacting with conduction car- riers, depends on the concentration of conduction carriers.

We have observed a phase transition at 22 K in the present sample. It is not clear, at present, whether both the 89 K and 22 K phase transitions take place in this sample consistent with our for- mer work.

Other measurements in this sample are in progress with different techniques and in different laboratory to confirm and to give a correct inter- pretation of these phase transitions.

References

/I/ Bierly, J.P., Muldawer, L. and Beclunan, O., Acta Metall. 2 (1963) 447.

121 Muldawer, L., Bull. Am. Phys. Soc. 16 (1971) 84.

131 Brillson,J.L., Burstein, E. and Muldawer, L., Phys. Rev. 2 (1974) 1547.

141 Iizumi, M., Hamaguchi, Y., Komatsubara, K.F. and Kato, Y., J. Phys. Soc. Japan 2 (1975) 443.

151 Kobayashi, K.L.I., Kato, Y., Katayama, Y. and Komatsubara, K.., Phys. Rev. Lett. 2 (1976) 772.

161 Fano, V., Fedeli, G. and Ortalli, I., Solid Sta- te Commun 22 (1977) 467.

/7/ Hatta, I. and Kobayashi, K.L.I., Solid State Commun 22 (1977) 775.

/81 Sugai, S., Murase, K. and Kawamura, H., Solid State Comun 2 (1977) 127.

/91 Katayama, S., Solid State Commun 19 (1976) 381.

/lo/ Sugai, S., Murase, K., Katayama, S., Takaoka,S., Nishi, S. and Kawamura, H., Solid State Commun 24 (1977) 407.

-

Acknowledgements.- We are indebted to Professor

I. Hatta for fruitful comments and discussions on

this work.