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Pressure-induced structural phase transition of iodine
,
Solid State C~imunications,Vol.30, pp.137—139. Pergamon Press Ltd. 1979. Printed in Great Britain.
PRESSURE-INDUCED STRUCTURAL PHASE TRANSITION OF IODINE K.Takemura, Y.Fujii and S.Minornura Ins titi~tefor Solid State Physic8, The University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan
and 0. Shimoinura Rational Institute for Researches in Inorganic Materials, Sakura-nna’a, Niihari-gun, Ibaraki 300-31, Japan (Received 29 January 1979 by H. Kawaiuura)
The structural phase transition of iodine was observed at about 210 kbar and at room temperature by the high-pressure x—ray diffraction technique using a diamond—anvil cell and a position—sensitive detector. It was found to occur reversibly in both processes of increasing and decreasing
pressure. 1. INTRODUCTION Iodine has been known as a prototype molecular crystal which exhibits a pres-
periment, iodine was found to undergo a structural phase transition. at about 210 kbar. The purpose of this paper is to report this newly observed phase tran-
sure—induced insulator-metal transition.
sition under pressure.
Measurements of the electrical resistivity1 and energy gap2 show that the metallization occurs gradually through 160180 kbar. From an interest in the mechanism of the metallization of iodine, present authors3 previously performed
2. EXPERIMENTA1~ The diamond-anvil cell used was the
same iodine as thatsample in ourwhich previous The puritystudy3’6. was given as 99.8% was obtained from Wako Pure Chemical Industries, Ltd. The sample was finely ground and crushed several times in order to eliminate a preferred
the structure analysis of it at 206 kbar in the metallic state. According to their experimental results, the shortest inter-molecular distance becomes compa-
rable to the intra-molecular
one (i.e.
bond-length) at 206 kbar belongs though the crystal structure still to the
orientation crystallites in the cell. As iodine is of reactive with such as iron in the air, it some was metals handled
same apace group, D18—Cmca, as that at atmospheric pressur~ The most remarkable feature is an elongation of the intra—molecular distance 0with increasing pressure (2.72 and 2.78 A at 1 bar and 206 kbar, respectively). This fact is recently the charge explained transferby between the mechanism neighbouring of molecules4. It is noted that the detailed structure analysis in such a high pressure region was performed with the sophisticated high—pressure x-ray diffraction technique using a position— sensitive detector (PSD) and a diamondanvil cell. This experimental result caused more interest in the metallization mechanism, so the present authors have continued the crystal structure analysis of iodine at several pressures around 180 kbar in the process of its metallization5. During the course of that ex-
in argon atmosphere. The sample was enclosed in a hole (0.3 am 0) of the Udiinet 700 gasket together with a small ruby chip for pressure measurement. Pressure calibration was done by the ruby R~line7.using A collimator the relation, withdA/dP= pin 0.365 A/kbar holes (0.15 imu 0, 0.2°divergence) was inserted in the diamond-anvil cell. It was adjusted so that the monochromatized x-ray beams ftlo-ka) passed through the center of the gasket hole to impinge only on the sample. The cell was mounted on a goniometer of the newly con— structed on—line—controlled high-pressure x—ray diffractoineter with a PSD specially designed for the Mo—ku radiation (ISSPXPSD system) 8 Prior to the measurement with the PSD, the Debye-Scherrer photograph was taken in order to confirm no existence of the appreciable preferred 137
138
STRUCTURAL PHASE TRANSITION OF IODINE
orientation of the sample. The PSD covered the scattering angle of 25° in a single measurement. All measurements were made at room temperature.
Vol.30, No.3 I
20
DINE
198 kbar
10 3. EXPERIMENTAL
RESULTS
The diffraction patterns of iodine were measured at several pressures around 200 kbar and they are shown in
0 20
Fig. 1 (l)-(6). The number of each figure specifies the sequence of the change of pressure in the present experiment. The new diffraction peaks marked with the triangles indicating an appearance of the high—pressure phase were observed at 198 kbar (1) and they became predominant at 240 kbar (2). As the pressure was released, the intensi— ties of these peaks gradually decreased ((3),(4)] and finally vanished at 166 kbar (5) while those of the low-pressure phase recovered. These diffraction pat terns of the low—pressure phase are sat— isfactorily explained by the space group
D~-cmca which is the same as that at atmospheric pressure9. Their indices are represented in the pattern at 166 kbar (5). When pressure was raised again up to 213 kbar (6), the high—pres sure phase appeared reproducibly.
10
0 “
220 kbar
20
.x ~ -____________________________ 0 20 U -~
~~86kbar >
10 -__________________________
z
[~]
Lii 20 4. DISCUSSION The present experimental results evidence an existence of the reversible structural phase transition of iodine at about 210 kbar. The high-pressure phase begins to appear at the pressure a little lower than 198 kbar in the process of increasing pressure (Pig.l(l)] while
it still remains at 186 kbar in the process of decreasing pressure [Fig.l (4)]. Both the high- and low—pressure phases seem to coexist in a rather wide range of pressure of at least 40 kbar. In such a high—pressure region, however, there is a pressure distribution comparable to that value in the sample on which x-ray beams (0.15 nun 0) impinge when the pressure—transmitting fluid is not used. In the present experiment, therefore, the definite transition pressure and pressure range of the coexistence of both phases cannot be obtained, The newly observed phase transition has stimulated an investigation of the relation between the transition and metallization process. The diffraction pattern of the high-pressure phase seems to be simpler than that of the low-pressure one. However, it has not been suc— cessfully solved yet. The experimental fact that the intensity ratio of two peaks at 26l5.2° and 19.4°changes considerably with pressure suggests the location of the iodine atom at the gen— eral position. This means that the structure of the high-pressure phase is
240 kbar
~
kbar
I.-. Z
10
g_; ~ ~
‘4
C 20
213
10 C 10
15
20
25
2 0 (deg.) Fig.l
—
30
35
Mo ka
X-ray diffraction patterns of iodine at several pressures. The peaks marked with triangles belong to the high—pressure phase while others to the low-pressure phase. The indices of those in the lowpressure phase are represented in the pattern at 166 kbar (5).
not such a simple lattice as face-centered or body—centered ones. The previous experimental result that no high-pressure phase3 was observed at 206 kbar is contrary to the present result. In the present experiment, the pressure was probably estimated to be lower by 20—30 kbar because the ruby chip was placed near the margin
Vol.30, No.3
STRUCTURAL PHASE TRANSITION OF IODINE
of the gasket hole where the pressure is
usually lower than that at the center. Then it is reasonable to consider that the previous experiment was made just below the critical pressure where the high-pressure phase begins to appear.
139
between the~pb~4etransition and metallization. In order to investigate it, the crystal structure analysis of the high-pressure phase is now in progress. AO~N0WLEDGEMENT
The phase transition of iodine newly
observed in the present experiment attracts much interest in the relation
The present work was supported by
the Grant—in-Aid for Scientific Research frcsn the Ministry of Education in Japan. REFERENCES
1. BALCHAN A.S. & DRI~KAMERH.G., J. Chem. Pkya. 34, 1948 (1961). 2. RIGGLEMAN B.M. & DRICKANER E.G., J. Chem. Phya. 38, 2721 (1963). 3 • SHIMOMT.JRA 0., TAXEMURA K •, FUJII Y., MINOMURA ~, MOP! M., NODA Y. & YAZIADA Y., Phys. Rev. BiB, 715 (1978).
4. KIICHI T., (private coxenunication). 5. TAKEMURA K., FUJII Y., SHIMOMTJRA 0. & MINOMURA S., (in preparation). 6. TAKEMURA K., SHIMOMURA 0. & MINOMURA S., (to be published in High Tenp.High Pressures). 7. PIERMARINI G.J., BLOCK S., BAPNETT J.D. & FORMAN R.A., J. Appl. Phys. 46, 2774 (1975). — 8. FtJJII Y., SHIMOMURA 0., TAKEMURA K., HOSHINO S. & MINOMURA S., (in preparation). 9. VAN BOLHUIS F., KOSTER P.B. & MIGEC}IELSEN T., ActaCrystallog. 23, 90 (1967).
Solid State C~imunications,Vol.30, pp.137—139. Pergamon Press Ltd. 1979. Printed in Great Britain.
PRESSURE-INDUCED STRUCTURAL PHASE TRANSITION OF IODINE K.Takemura, Y.Fujii and S.Minornura Ins titi~tefor Solid State Physic8, The University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan
and 0. Shimoinura Rational Institute for Researches in Inorganic Materials, Sakura-nna’a, Niihari-gun, Ibaraki 300-31, Japan (Received 29 January 1979 by H. Kawaiuura)
The structural phase transition of iodine was observed at about 210 kbar and at room temperature by the high-pressure x—ray diffraction technique using a diamond—anvil cell and a position—sensitive detector. It was found to occur reversibly in both processes of increasing and decreasing
pressure. 1. INTRODUCTION Iodine has been known as a prototype molecular crystal which exhibits a pres-
periment, iodine was found to undergo a structural phase transition. at about 210 kbar. The purpose of this paper is to report this newly observed phase tran-
sure—induced insulator-metal transition.
sition under pressure.
Measurements of the electrical resistivity1 and energy gap2 show that the metallization occurs gradually through 160180 kbar. From an interest in the mechanism of the metallization of iodine, present authors3 previously performed
2. EXPERIMENTA1~ The diamond-anvil cell used was the
same iodine as thatsample in ourwhich previous The puritystudy3’6. was given as 99.8% was obtained from Wako Pure Chemical Industries, Ltd. The sample was finely ground and crushed several times in order to eliminate a preferred
the structure analysis of it at 206 kbar in the metallic state. According to their experimental results, the shortest inter-molecular distance becomes compa-
rable to the intra-molecular
one (i.e.
bond-length) at 206 kbar belongs though the crystal structure still to the
orientation crystallites in the cell. As iodine is of reactive with such as iron in the air, it some was metals handled
same apace group, D18—Cmca, as that at atmospheric pressur~ The most remarkable feature is an elongation of the intra—molecular distance 0with increasing pressure (2.72 and 2.78 A at 1 bar and 206 kbar, respectively). This fact is recently the charge explained transferby between the mechanism neighbouring of molecules4. It is noted that the detailed structure analysis in such a high pressure region was performed with the sophisticated high—pressure x-ray diffraction technique using a position— sensitive detector (PSD) and a diamondanvil cell. This experimental result caused more interest in the metallization mechanism, so the present authors have continued the crystal structure analysis of iodine at several pressures around 180 kbar in the process of its metallization5. During the course of that ex-
in argon atmosphere. The sample was enclosed in a hole (0.3 am 0) of the Udiinet 700 gasket together with a small ruby chip for pressure measurement. Pressure calibration was done by the ruby R~line7.using A collimator the relation, withdA/dP= pin 0.365 A/kbar holes (0.15 imu 0, 0.2°divergence) was inserted in the diamond-anvil cell. It was adjusted so that the monochromatized x-ray beams ftlo-ka) passed through the center of the gasket hole to impinge only on the sample. The cell was mounted on a goniometer of the newly con— structed on—line—controlled high-pressure x—ray diffractoineter with a PSD specially designed for the Mo—ku radiation (ISSPXPSD system) 8 Prior to the measurement with the PSD, the Debye-Scherrer photograph was taken in order to confirm no existence of the appreciable preferred 137
138
STRUCTURAL PHASE TRANSITION OF IODINE
orientation of the sample. The PSD covered the scattering angle of 25° in a single measurement. All measurements were made at room temperature.
Vol.30, No.3 I
20
DINE
198 kbar
10 3. EXPERIMENTAL
RESULTS
The diffraction patterns of iodine were measured at several pressures around 200 kbar and they are shown in
0 20
Fig. 1 (l)-(6). The number of each figure specifies the sequence of the change of pressure in the present experiment. The new diffraction peaks marked with the triangles indicating an appearance of the high—pressure phase were observed at 198 kbar (1) and they became predominant at 240 kbar (2). As the pressure was released, the intensi— ties of these peaks gradually decreased ((3),(4)] and finally vanished at 166 kbar (5) while those of the low-pressure phase recovered. These diffraction pat terns of the low—pressure phase are sat— isfactorily explained by the space group
D~-cmca which is the same as that at atmospheric pressure9. Their indices are represented in the pattern at 166 kbar (5). When pressure was raised again up to 213 kbar (6), the high—pres sure phase appeared reproducibly.
10
0 “
220 kbar
20
.x ~ -____________________________ 0 20 U -~
~~86kbar >
10 -__________________________
z
[~]
Lii 20 4. DISCUSSION The present experimental results evidence an existence of the reversible structural phase transition of iodine at about 210 kbar. The high-pressure phase begins to appear at the pressure a little lower than 198 kbar in the process of increasing pressure (Pig.l(l)] while
it still remains at 186 kbar in the process of decreasing pressure [Fig.l (4)]. Both the high- and low—pressure phases seem to coexist in a rather wide range of pressure of at least 40 kbar. In such a high—pressure region, however, there is a pressure distribution comparable to that value in the sample on which x-ray beams (0.15 nun 0) impinge when the pressure—transmitting fluid is not used. In the present experiment, therefore, the definite transition pressure and pressure range of the coexistence of both phases cannot be obtained, The newly observed phase transition has stimulated an investigation of the relation between the transition and metallization process. The diffraction pattern of the high-pressure phase seems to be simpler than that of the low-pressure one. However, it has not been suc— cessfully solved yet. The experimental fact that the intensity ratio of two peaks at 26l5.2° and 19.4°changes considerably with pressure suggests the location of the iodine atom at the gen— eral position. This means that the structure of the high-pressure phase is
240 kbar
~
kbar
I.-. Z
10
g_; ~ ~
‘4
C 20
213
10 C 10
15
20
25
2 0 (deg.) Fig.l
—
30
35
Mo ka
X-ray diffraction patterns of iodine at several pressures. The peaks marked with triangles belong to the high—pressure phase while others to the low-pressure phase. The indices of those in the lowpressure phase are represented in the pattern at 166 kbar (5).
not such a simple lattice as face-centered or body—centered ones. The previous experimental result that no high-pressure phase3 was observed at 206 kbar is contrary to the present result. In the present experiment, the pressure was probably estimated to be lower by 20—30 kbar because the ruby chip was placed near the margin
Vol.30, No.3
STRUCTURAL PHASE TRANSITION OF IODINE
of the gasket hole where the pressure is
usually lower than that at the center. Then it is reasonable to consider that the previous experiment was made just below the critical pressure where the high-pressure phase begins to appear.
139
between the~pb~4etransition and metallization. In order to investigate it, the crystal structure analysis of the high-pressure phase is now in progress. AO~N0WLEDGEMENT
The phase transition of iodine newly
observed in the present experiment attracts much interest in the relation
The present work was supported by
the Grant—in-Aid for Scientific Research frcsn the Ministry of Education in Japan. REFERENCES
1. BALCHAN A.S. & DRI~KAMERH.G., J. Chem. Pkya. 34, 1948 (1961). 2. RIGGLEMAN B.M. & DRICKANER E.G., J. Chem. Phya. 38, 2721 (1963). 3 • SHIMOMT.JRA 0., TAXEMURA K •, FUJII Y., MINOMURA ~, MOP! M., NODA Y. & YAZIADA Y., Phys. Rev. BiB, 715 (1978).
4. KIICHI T., (private coxenunication). 5. TAKEMURA K., FUJII Y., SHIMOMTJRA 0. & MINOMURA S., (in preparation). 6. TAKEMURA K., SHIMOMURA 0. & MINOMURA S., (to be published in High Tenp.High Pressures). 7. PIERMARINI G.J., BLOCK S., BAPNETT J.D. & FORMAN R.A., J. Appl. Phys. 46, 2774 (1975). — 8. FtJJII Y., SHIMOMURA 0., TAKEMURA K., HOSHINO S. & MINOMURA S., (in preparation). 9. VAN BOLHUIS F., KOSTER P.B. & MIGEC}IELSEN T., ActaCrystallog. 23, 90 (1967).