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A new long period superstructure in Pt3V
Mat. Res. Bull., Vol. 19, pp. 979-982, 1984. Printed in the USA. 0025-5408/84 $3.00 + .00 C o p y r i g h t (c) 1984 Pergamon P r e s s Ltd.
A NEW LONG PERIOD SUPERSTRUCTURE
University
of
IN Pt3V
D.Schryvers and S.Amelinckx 1 Antwerp,RUCA,Groenenborgerlaan,171.B-2020 l)Also at : SCK, B-2400 Mol, Belgium
Antwerpen,
Belgium
(Received April 20, 1984; Refereed)
ABSTRACT. Under certain conditions the alloy Pt3V exhibits a body centered tetragonal long period anti-phase boundary superstructure with lattice parameter a = a 0 and c = 8a0, which is a derivative of the D022 structure. This phase is observed as a transition structure between the high and the low temperature phases of composition Pt3V.
During a recent re-examlnatlon of the ordered phases in the alloy system Pt-V, we have found a number of new structural features. In particular it was discovered that the alloy with composition Pt8V is isostructural with Pt8Ti (1)(2). The alloy with composition Pt3V is described in the literature (3) as having the Cu3Au structure at high temperature (1000°C) and the D022 structure at lower temperature (900°C). We have re-examined this alloy in some detail, using selected area electron diffraction and high resolution electron microscopy. In the course of this study we have discovered a new long period structure, which we shall now describe. The new phase is found in an alloy with nominal composition Pt3V and which was quenched from II00°C and subsequently annealed during 30 min at 900°C. On prolonged annealing at that temperature the structure becomes ultimately D022 in agreement with the literature (3). Under these conditions the new structure is then a "transition" structure; it has not yet been determined whether or not and under which conditions the structure might be stable. The diffraction pattern of a single variant, along a cube zone, shown in fig la, is reproduced in fig.lb. It is quite clear that the most intense spots are located at, or occur in the vicinity of the D022 spots marked by crosses. This strongly suggests that the superstructure must be a derivative of the D022 structure. The i01 and 103 reflections of the D022 structure are split in
Work performed under the auspices cial support of the IIKW.
of the association
979
RUCA-SCK
and with finan-
980
D. S C H R Y V E R S ,
et al.
Vo]. 19, No. 8
200
202
®
[
204
®
X
101
103
exe
exe
V2
®
x
®
000
002
0O4
Fig.l a) Cube zone diffraction pattern of the new long period superstructure of the D022 structure. Note that intense spots are concentrated at and around D022 spot positions. b) Schematic representation of a quandrant of the diffraction pattern of fig. la. The DO22 spot positions are indicated by crosses; the i01 and 103 spots are split.
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APB
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.
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C Ip"
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i° DO22
L12
Fig.2. Model of the long period superstructure. The full and open dots represent V atoms at levels O and 1/2 respectively. The antl-phase boundaries are indicated as well. two "satellites" their separation being nearly equal to 1/4 of the length of the diffraction vector 002. The splitting is symmetrical with respect to the D022 spot positions, i.e. the fractional shifts are ±1/2 (4). There are no fractional shifts for the 002 and 202 spots. The observed fractional shifts are summarized in table I and are represented in fig.l.b. In a number of previous papers the method of"fractional shifts" for the determination of long period anti-phase boundary structures, from the geometry
Vol. 19, No. 8
Pt3V STRUCTURE
981
TABLE I
g Observed (mod.l) 002 200 004 101 103
0 0 0
1/2 1/2
Calculated (mod.l) 0 I 0 1/2 1/2
of the diffraction pattern, was explained and its use demonstrated (1,2). We applied this method also to the present case. One finds: l) The basic structure is the D022 structure (from the positions of the most intense spots). 2) The anti-phase boundaries are perpendicular to the [OO11 direction of the D022 structure (from the orientation of the satellite sequences). 3) The distance between anti-phase boundaries is equal to two times the c-axls of the D022 structure (from the separation of the satellite spots). 4) The displacement vector of the antl-phase boundaries is 1/2[llO]D022 (from the fractional shifts). In table I it is shown that the calculated fractional shifts are consistent with the observed ones.
Flg.3. High resolution electron microscopic image of the new long period superstructure. The bright dots correspond with vanadium columns. Fig.2 represents a model which is in agreement with all the observed features of the diffraction pattern. Only the vanadium atoms are shown. It is clearly a long period superstructure of the D022 structure. Along the antiphase boundaries, which are all identical and conservative, the atom configurations are those of the CusAu structure. The structure is thus a mixture of structure elements of the high temperature and low temperature phases;it can best be described with reference to a body centered tetragonal Bravais lattice with lattice parameters a i d = a 0 = ~0.4nm; Cl_= 8a~.(a 0 is the lattice I i is u indicated in fig.2. parameter of the underlying ~CC lattice).The unit Pce
982
D. SCHRYVERS, et al.
Vol. 19, No. 8
We have confirmed this structure by means of high resolution images, made by using the bright field superstructure imaging mode, i . e . including the direct beam, the first shell of FCC spots and all superstructure spots within this first shell. Fig.3 shows an image taken along the [I00] direction. Under the imaging conditions used, the bright dots represent the light minority atom columns, i.e. the vanadium columns. The correspondance between the image and the model is quite obvious. The structure often exhibits defects, such as extra atom layers in the DO22 strips, as indicated by arrows in flg.3. This results in a somewhat variable average spacing between anti-phase boundaries and in pseudo incommensurate diffraction patterns. References. l.D.Schryvers, J.Van Landuyt, G.Van Tendeloo and S.Amellnckx,Phys.Stat.Sol.(a) 76, 575 (1983). 2.D.Schryvers, J.Van Landuyt,S.Amelinckx, Mat.Res.Bull.18,1369(1983). 3.A.Maldonado and K. Schubert, Z.Metallk. 55, 619 (1964). R.M. Waterstrat, Met.Trans. 4, 455 (197~. 4.J.Van Landuyt, R.De Ridder, R.Gevers,S.Amelinckx,Mat.Res.Bull.~,353(1970).
A NEW LONG PERIOD SUPERSTRUCTURE
University
of
IN Pt3V
D.Schryvers and S.Amelinckx 1 Antwerp,RUCA,Groenenborgerlaan,171.B-2020 l)Also at : SCK, B-2400 Mol, Belgium
Antwerpen,
Belgium
(Received April 20, 1984; Refereed)
ABSTRACT. Under certain conditions the alloy Pt3V exhibits a body centered tetragonal long period anti-phase boundary superstructure with lattice parameter a = a 0 and c = 8a0, which is a derivative of the D022 structure. This phase is observed as a transition structure between the high and the low temperature phases of composition Pt3V.
During a recent re-examlnatlon of the ordered phases in the alloy system Pt-V, we have found a number of new structural features. In particular it was discovered that the alloy with composition Pt8V is isostructural with Pt8Ti (1)(2). The alloy with composition Pt3V is described in the literature (3) as having the Cu3Au structure at high temperature (1000°C) and the D022 structure at lower temperature (900°C). We have re-examined this alloy in some detail, using selected area electron diffraction and high resolution electron microscopy. In the course of this study we have discovered a new long period structure, which we shall now describe. The new phase is found in an alloy with nominal composition Pt3V and which was quenched from II00°C and subsequently annealed during 30 min at 900°C. On prolonged annealing at that temperature the structure becomes ultimately D022 in agreement with the literature (3). Under these conditions the new structure is then a "transition" structure; it has not yet been determined whether or not and under which conditions the structure might be stable. The diffraction pattern of a single variant, along a cube zone, shown in fig la, is reproduced in fig.lb. It is quite clear that the most intense spots are located at, or occur in the vicinity of the D022 spots marked by crosses. This strongly suggests that the superstructure must be a derivative of the D022 structure. The i01 and 103 reflections of the D022 structure are split in
Work performed under the auspices cial support of the IIKW.
of the association
979
RUCA-SCK
and with finan-
980
D. S C H R Y V E R S ,
et al.
Vo]. 19, No. 8
200
202
®
[
204
®
X
101
103
exe
exe
V2
®
x
®
000
002
0O4
Fig.l a) Cube zone diffraction pattern of the new long period superstructure of the D022 structure. Note that intense spots are concentrated at and around D022 spot positions. b) Schematic representation of a quandrant of the diffraction pattern of fig. la. The DO22 spot positions are indicated by crosses; the i01 and 103 spots are split.
APB
APB
".+i. 1
alpT •
t
i---
APB
"÷ --
-.
0 - .
.
.
.
-0-
."+i.
- -0-
. . . .
-0--
---1
I
I •
w
<>- . . . .
-O- --O- . . . .
-O---
-- J
)
C Ip"
8ao
ao
i° DO22
L12
Fig.2. Model of the long period superstructure. The full and open dots represent V atoms at levels O and 1/2 respectively. The antl-phase boundaries are indicated as well. two "satellites" their separation being nearly equal to 1/4 of the length of the diffraction vector 002. The splitting is symmetrical with respect to the D022 spot positions, i.e. the fractional shifts are ±1/2 (4). There are no fractional shifts for the 002 and 202 spots. The observed fractional shifts are summarized in table I and are represented in fig.l.b. In a number of previous papers the method of"fractional shifts" for the determination of long period anti-phase boundary structures, from the geometry
Vol. 19, No. 8
Pt3V STRUCTURE
981
TABLE I
g Observed (mod.l) 002 200 004 101 103
0 0 0
1/2 1/2
Calculated (mod.l) 0 I 0 1/2 1/2
of the diffraction pattern, was explained and its use demonstrated (1,2). We applied this method also to the present case. One finds: l) The basic structure is the D022 structure (from the positions of the most intense spots). 2) The anti-phase boundaries are perpendicular to the [OO11 direction of the D022 structure (from the orientation of the satellite sequences). 3) The distance between anti-phase boundaries is equal to two times the c-axls of the D022 structure (from the separation of the satellite spots). 4) The displacement vector of the antl-phase boundaries is 1/2[llO]D022 (from the fractional shifts). In table I it is shown that the calculated fractional shifts are consistent with the observed ones.
Flg.3. High resolution electron microscopic image of the new long period superstructure. The bright dots correspond with vanadium columns. Fig.2 represents a model which is in agreement with all the observed features of the diffraction pattern. Only the vanadium atoms are shown. It is clearly a long period superstructure of the D022 structure. Along the antiphase boundaries, which are all identical and conservative, the atom configurations are those of the CusAu structure. The structure is thus a mixture of structure elements of the high temperature and low temperature phases;it can best be described with reference to a body centered tetragonal Bravais lattice with lattice parameters a i d = a 0 = ~0.4nm; Cl_= 8a~.(a 0 is the lattice I i is u indicated in fig.2. parameter of the underlying ~CC lattice).The unit Pce
982
D. SCHRYVERS, et al.
Vol. 19, No. 8
We have confirmed this structure by means of high resolution images, made by using the bright field superstructure imaging mode, i . e . including the direct beam, the first shell of FCC spots and all superstructure spots within this first shell. Fig.3 shows an image taken along the [I00] direction. Under the imaging conditions used, the bright dots represent the light minority atom columns, i.e. the vanadium columns. The correspondance between the image and the model is quite obvious. The structure often exhibits defects, such as extra atom layers in the DO22 strips, as indicated by arrows in flg.3. This results in a somewhat variable average spacing between anti-phase boundaries and in pseudo incommensurate diffraction patterns. References. l.D.Schryvers, J.Van Landuyt, G.Van Tendeloo and S.Amellnckx,Phys.Stat.Sol.(a) 76, 575 (1983). 2.D.Schryvers, J.Van Landuyt,S.Amelinckx, Mat.Res.Bull.18,1369(1983). 3.A.Maldonado and K. Schubert, Z.Metallk. 55, 619 (1964). R.M. Waterstrat, Met.Trans. 4, 455 (197~. 4.J.Van Landuyt, R.De Ridder, R.Gevers,S.Amelinckx,Mat.Res.Bull.~,353(1970).