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Polytypism of alpha-LiNH4SO4 crystals
~)
Solid State Communications, Vol. 81, No. 4, pp. 333-335, 1992. Printed in Great Britain.
0038-1098/9255.00+.00 Pergamon Press plc
POLYTYPISM OF ALPHA-LiNH4SO 4 CRYSTALS Pawef E. Tomaszewski
I n s t i t u t e o f Low Temperature and S t r u c t u r e Research, Polish Academy o f Sciences, P.O.Box 937, 50-950 Wroctaw, Poland
(Received 17 June 1991 by M. Balkanski)
The X-ray diffraction studies were made on different polytypes of ~ modification of LiNH4S04 crystal. There exists at least three polytyplc modifications whose adequate nomenclature is proposed (2 Or, 4 M, 6 Or). Two first polytypes exhibit also partially disordered stacking sequence providing to diffuse streaks running in the reciprocal lattice perpendicularly to layers forming the crystal structure.
The LiNH4S04 compound crystallizes in two, called as a and 8, modifications known since 1867 [I]. Contrary to well studied ~ modification, there are in literature only three old original papers devoted to ~ modification [I,2,3] and two unpublished thesis with a small parts about this crystal [4,5]. Quite recently new interesting studies were made by Hilczer, Sosnowska, Pietraszko and their co-workers providing a few confusing results [6]. This shows a necessity of further intense studies on the crystal properties and physical characterization of both, ~ and 8, polymorphs of LiNI~S04. Thus the X-ray diffraction studies revealing the existence of polytyplsm is a subject of presented paper. As a consequence, the adequate nomenclature of ~-LINH4S04 is proposed. The ~ modification of LINH4S04 can be grown by evaporation from water solution at the temperature inferior than about 297 K [1,3,4,6]. Above %hls temperature the modification is the one growing crystal. In my studies the crystals used as a samples were grown in different laboratories within the period of 1979-1989. Unfortunately, it is not possible now to describe in details the conditions of their growth and to correlate them wlth the observed physical properties.
c = 10.4A was chosen. Polytypic structures are then realized by stacking a layers exlstlng in the crystal structure [8] along a-axls leading to the multiplication of lattice parameter a. There exists at least three polytyplc modifications of ~-LINH4S04. Using the Ramsdel notation [7] these polytypes may be named as 2 Or, 4 M and 6 Or where the number indicate the quantity of superimposed layers, Or and M stand for orthorhombic and monoclinic symmetry respectively. The results of my experiments on ~-LiNH4S04 as well as data from literature [4,8-13] are reviewed in the Table below. The data for LINH~Se04 was also added for comparison. The space groups were deduced from the systematic extinctions observed on Welssenberg photographs. Additional extinctions can be correlated with the sequence of layers in each polytyplc modification. All three polytypes have the same diffraction patterns on hkZ [with ~ even)Weissenberg photographs. The ~u~l-layer [with ~ odd) photographs are characteristic for each polytype. Thus, even for mixed samples the reflections from different polytypes are well separate (no overlapping reflections for odd-layers) and can be directly used for structure determination of each polytype. The basic polytype 207" wlth the smallest a-perlod is orthorhomblc [I,3,4,5,8,11] with the space group P2,ca (N~ 29) confirmed by full structure determination [8]. The most of as-grown crystals are mixed wlth another polytype. Its characteristic superstructure reflections are non-equlvalent in intensity indicating the slight monocllnlclty in spite of lattice remaining still orthorhombic with doubled lattice parameter a. The space group of this 4M polytype is Pl21/ul or Pl2,/cl (N~ 14).
All X-ray diffraction patterns (from powdered samples as well as from single crystal) come from only one, ~ modification. There are no evidence for biphase (~ and 8) state of studied samples. However, careful inspection of Welssenberg photographs shows the existence of a certain number of supplementary superstructure reflections -- different for different samples -- in the same direction in the reciprocal lattlce, a'. This leads to the possible explanation of such diffraction patterns in terms of polytyplsm [5,7]. Thus, the so-called basic structure with the smallest unit cell of orthorhomblc symmetry and lattice parameters of about a = 17.00A, b=4.96~ and
Thus the diffraction pattern of as-grown crystals consists of superposltion of patterns characteristic for both, 2 0 r and 4 M , polytypes. Gradual change of reflection intensity
333
334
POLYTYPISM OF ALPHA-LiNH4SO 4 CRYSTALS
TabLe
pound I
LAS
I.
Lattice
I Com-INam e
Na
Space group
parameters 2 Or
Vol. 81, No. 4
Diff.
Samples b
scarf.
17-5-I0 c
I
Pmca or P21ca
Yes
[4][9]
d PZ,ca (29] Yes this work (A,B];[8] ....................................................................................................................................... LASe
e
Pnma P.ca
(62)
[I0] [11]
PZ,ca LAS
4 M
34-5-10
2
4 Or [ps:eudo]
LASe
4 Or
LAS
6 Or
a b
-- N = superstructure
3
index
unique axis a
[13] [4] g
Pl2,/al Pl2,/cl
or (14)
Yes
this work
B,(ac).
h
Yes
thls work
Bmam
Yes
[8]
Bmam
Yes
[12]
No
thls work
Pcca
(54]
(multiplication
(A,B)
(C)
of lattice along u-axls)
-- the letters denote the source of the samples: A - our Institute (grown in 1979), B and C - Unlverslt4 Parls-Nord [(1984) and (1987), respectively]
c _
d
51-5-10
Yes
a = 16.994, b = 5 . 0 7 8 , c = 9 . 9 5 3 a = 17.06, b = 5 . 1 0 2 , c=9.985 diffractometer (at 2 9 5 K )
-- a = 17.1053, b = 4 . 9 9 1 7 , diffractometry
~ from photographs, ~ after refinement
c =9.9824
A
from
single
from
powder
crystal
e _ a = 17.390, b = 5 . 1 0 , c = 1 0 . 6 4 f -- a = 1 7 . 4 2 4 , b = 5 . 1 2 3 , c = I 0 . 5 6 7 g -- superstructure reflections observed after one year of 20~" sample stacking h -- Bma2, B2cm (39) or Bmam, Bmcm (67)
observed for different samples (see Flg. l. showing a part of hll row of reflections indexed in basic 2 Or polytype) corresponds to changes of amount of both constituent phases. Wlth the growing amount of 4 M polytype from one sample to the other, its reflections become more intense and more narrow up to pure 4 H polytype. No time effect was observed even within a few years contrary to data in [4]. Sample
411
311
211
2 Or A
0 0 0
0 0 0
o o o
B B
o o o
B, 4 M C, 6 O r C
o o
o
F~g.
i.
o o o o o
The bottom part of Fig. l. shows a part of hll row from the samples C which could be interpreted as a mixture of leftand right-handed orientations of 6 Or polytype (probable space group P c c u (N~ 54)). The X-ray single crystal photographs made on A, B samples show, besides the well pronounced r e f l e c t i o n s from ordered phases 2 Or and 4 M, the diffuse streaks runnlnE In the reciprocal lattice along a*. They indicate the existence in the sample the one-dlmensional disorder resultln E from a certain amount of randomly stocked layers [7]. The mixed presence of an order and disorder is an another characteristic feature of many polytyplc crystals. It should be noticed that there Is no time effect (verified on the sample B) on the diffuse scatterln E - the diffraction pattern remains unchangeable even after a few years contrary to the observations made in [4]. The diffuse scattering was not observed for C-samples wlth the 3u superstructure (6 Or polytype).
Vol. 81, No. 4
POLYTYPISM OF ALPHA-LiNH4SO 4 CRYSTALS
The suggestion about isomorphism between =-LINH4S04 and LINH4Se04 is very interesting and requires the search for similar polytyplc behavlour [5]. The first inspection of LINH4Se04 samples shows the existence of 2 Or and 4 0 r polytypes [13].
2. 3. 4. 5.
Acknowledgement I would like to thank Mrs. J.Kalicifiska-Karut (our Institute) for preparing the samples of type A, Dr. M. Quilichlni (Universit4 ParisNord, Vllletaneuse, France) for supplying the good crystals of type B and C and to Dr. A. Pletraszko (our Institute) for their results on crystals grown by Prof. B. Hllczer (Institute of Molecular Physics, Poznafi, Poland) prior to Its publication. Finally, I would like to thank Dr. A. Pietraszko for valuable and fruitful discussions during the studies on ~-LiNH4S04.
A. S c a c c h l ,
7.
8. 9. 10. 11. 12. 13.
Re~rences I.
6.
Att~
d . ~ . A c c a d . d . S c L F t s . Mat.
335
3 ( 2 7 ) , 1 (1868) G. Wyrouboff, BuII.Soc. Htn. F r a n c e S, 35 (1882) G. Wyrouboff, Bull.Soc. M~n. F r a n c e 13, 215 (1890) B.O. Hlldmann, PhD T h e s i s , TH Aachen (1980) P.E. Tomaszewskl, PhD Thesis, INTIBS PAN Wroct aw (1985) I.Sosnowska, B. Hilczer & P. Piskunowlcz, Soi~d State Commun. 74, 1249 (1990) A.R. Verma & P. Krlshna, polymorphLsm and potytyp(sm (n crystals, Wiley & Sons, New York (1966) A. Pletraszko & K.~.ukaszewicz, to be pub I ished. B.O. Hlldmann & Th. Hahn (1977), in: Powder D~ffraction F~le, No. 29-795 (1987) P. Brenner (1969), in: S.J.Chung: PhD Thesis, TH Aachen {1972}. J.Gllnnemann & Th. Hahn (1977), in: Powder D~ffructLon F£Le, No. 29-794 (1987) T. LIs (1980), private information A. Pletraszko & 3. St~ple~-Damm, private communication
Solid State Communications, Vol. 81, No. 4, pp. 333-335, 1992. Printed in Great Britain.
0038-1098/9255.00+.00 Pergamon Press plc
POLYTYPISM OF ALPHA-LiNH4SO 4 CRYSTALS Pawef E. Tomaszewski
I n s t i t u t e o f Low Temperature and S t r u c t u r e Research, Polish Academy o f Sciences, P.O.Box 937, 50-950 Wroctaw, Poland
(Received 17 June 1991 by M. Balkanski)
The X-ray diffraction studies were made on different polytypes of ~ modification of LiNH4S04 crystal. There exists at least three polytyplc modifications whose adequate nomenclature is proposed (2 Or, 4 M, 6 Or). Two first polytypes exhibit also partially disordered stacking sequence providing to diffuse streaks running in the reciprocal lattice perpendicularly to layers forming the crystal structure.
The LiNH4S04 compound crystallizes in two, called as a and 8, modifications known since 1867 [I]. Contrary to well studied ~ modification, there are in literature only three old original papers devoted to ~ modification [I,2,3] and two unpublished thesis with a small parts about this crystal [4,5]. Quite recently new interesting studies were made by Hilczer, Sosnowska, Pietraszko and their co-workers providing a few confusing results [6]. This shows a necessity of further intense studies on the crystal properties and physical characterization of both, ~ and 8, polymorphs of LiNI~S04. Thus the X-ray diffraction studies revealing the existence of polytyplsm is a subject of presented paper. As a consequence, the adequate nomenclature of ~-LINH4S04 is proposed. The ~ modification of LINH4S04 can be grown by evaporation from water solution at the temperature inferior than about 297 K [1,3,4,6]. Above %hls temperature the modification is the one growing crystal. In my studies the crystals used as a samples were grown in different laboratories within the period of 1979-1989. Unfortunately, it is not possible now to describe in details the conditions of their growth and to correlate them wlth the observed physical properties.
c = 10.4A was chosen. Polytypic structures are then realized by stacking a layers exlstlng in the crystal structure [8] along a-axls leading to the multiplication of lattice parameter a. There exists at least three polytyplc modifications of ~-LINH4S04. Using the Ramsdel notation [7] these polytypes may be named as 2 Or, 4 M and 6 Or where the number indicate the quantity of superimposed layers, Or and M stand for orthorhombic and monoclinic symmetry respectively. The results of my experiments on ~-LiNH4S04 as well as data from literature [4,8-13] are reviewed in the Table below. The data for LINH~Se04 was also added for comparison. The space groups were deduced from the systematic extinctions observed on Welssenberg photographs. Additional extinctions can be correlated with the sequence of layers in each polytyplc modification. All three polytypes have the same diffraction patterns on hkZ [with ~ even)Weissenberg photographs. The ~u~l-layer [with ~ odd) photographs are characteristic for each polytype. Thus, even for mixed samples the reflections from different polytypes are well separate (no overlapping reflections for odd-layers) and can be directly used for structure determination of each polytype. The basic polytype 207" wlth the smallest a-perlod is orthorhomblc [I,3,4,5,8,11] with the space group P2,ca (N~ 29) confirmed by full structure determination [8]. The most of as-grown crystals are mixed wlth another polytype. Its characteristic superstructure reflections are non-equlvalent in intensity indicating the slight monocllnlclty in spite of lattice remaining still orthorhombic with doubled lattice parameter a. The space group of this 4M polytype is Pl21/ul or Pl2,/cl (N~ 14).
All X-ray diffraction patterns (from powdered samples as well as from single crystal) come from only one, ~ modification. There are no evidence for biphase (~ and 8) state of studied samples. However, careful inspection of Welssenberg photographs shows the existence of a certain number of supplementary superstructure reflections -- different for different samples -- in the same direction in the reciprocal lattlce, a'. This leads to the possible explanation of such diffraction patterns in terms of polytyplsm [5,7]. Thus, the so-called basic structure with the smallest unit cell of orthorhomblc symmetry and lattice parameters of about a = 17.00A, b=4.96~ and
Thus the diffraction pattern of as-grown crystals consists of superposltion of patterns characteristic for both, 2 0 r and 4 M , polytypes. Gradual change of reflection intensity
333
334
POLYTYPISM OF ALPHA-LiNH4SO 4 CRYSTALS
TabLe
pound I
LAS
I.
Lattice
I Com-INam e
Na
Space group
parameters 2 Or
Vol. 81, No. 4
Diff.
Samples b
scarf.
17-5-I0 c
I
Pmca or P21ca
Yes
[4][9]
d PZ,ca (29] Yes this work (A,B];[8] ....................................................................................................................................... LASe
e
Pnma P.ca
(62)
[I0] [11]
PZ,ca LAS
4 M
34-5-10
2
4 Or [ps:eudo]
LASe
4 Or
LAS
6 Or
a b
-- N = superstructure
3
index
unique axis a
[13] [4] g
Pl2,/al Pl2,/cl
or (14)
Yes
this work
B,(ac).
h
Yes
thls work
Bmam
Yes
[8]
Bmam
Yes
[12]
No
thls work
Pcca
(54]
(multiplication
(A,B)
(C)
of lattice along u-axls)
-- the letters denote the source of the samples: A - our Institute (grown in 1979), B and C - Unlverslt4 Parls-Nord [(1984) and (1987), respectively]
c _
d
51-5-10
Yes
a = 16.994, b = 5 . 0 7 8 , c = 9 . 9 5 3 a = 17.06, b = 5 . 1 0 2 , c=9.985 diffractometer (at 2 9 5 K )
-- a = 17.1053, b = 4 . 9 9 1 7 , diffractometry
~ from photographs, ~ after refinement
c =9.9824
A
from
single
from
powder
crystal
e _ a = 17.390, b = 5 . 1 0 , c = 1 0 . 6 4 f -- a = 1 7 . 4 2 4 , b = 5 . 1 2 3 , c = I 0 . 5 6 7 g -- superstructure reflections observed after one year of 20~" sample stacking h -- Bma2, B2cm (39) or Bmam, Bmcm (67)
observed for different samples (see Flg. l. showing a part of hll row of reflections indexed in basic 2 Or polytype) corresponds to changes of amount of both constituent phases. Wlth the growing amount of 4 M polytype from one sample to the other, its reflections become more intense and more narrow up to pure 4 H polytype. No time effect was observed even within a few years contrary to data in [4]. Sample
411
311
211
2 Or A
0 0 0
0 0 0
o o o
B B
o o o
B, 4 M C, 6 O r C
o o
o
F~g.
i.
o o o o o
The bottom part of Fig. l. shows a part of hll row from the samples C which could be interpreted as a mixture of leftand right-handed orientations of 6 Or polytype (probable space group P c c u (N~ 54)). The X-ray single crystal photographs made on A, B samples show, besides the well pronounced r e f l e c t i o n s from ordered phases 2 Or and 4 M, the diffuse streaks runnlnE In the reciprocal lattice along a*. They indicate the existence in the sample the one-dlmensional disorder resultln E from a certain amount of randomly stocked layers [7]. The mixed presence of an order and disorder is an another characteristic feature of many polytyplc crystals. It should be noticed that there Is no time effect (verified on the sample B) on the diffuse scatterln E - the diffraction pattern remains unchangeable even after a few years contrary to the observations made in [4]. The diffuse scattering was not observed for C-samples wlth the 3u superstructure (6 Or polytype).
Vol. 81, No. 4
POLYTYPISM OF ALPHA-LiNH4SO 4 CRYSTALS
The suggestion about isomorphism between =-LINH4S04 and LINH4Se04 is very interesting and requires the search for similar polytyplc behavlour [5]. The first inspection of LINH4Se04 samples shows the existence of 2 Or and 4 0 r polytypes [13].
2. 3. 4. 5.
Acknowledgement I would like to thank Mrs. J.Kalicifiska-Karut (our Institute) for preparing the samples of type A, Dr. M. Quilichlni (Universit4 ParisNord, Vllletaneuse, France) for supplying the good crystals of type B and C and to Dr. A. Pletraszko (our Institute) for their results on crystals grown by Prof. B. Hllczer (Institute of Molecular Physics, Poznafi, Poland) prior to Its publication. Finally, I would like to thank Dr. A. Pietraszko for valuable and fruitful discussions during the studies on ~-LiNH4S04.
A. S c a c c h l ,
7.
8. 9. 10. 11. 12. 13.
Re~rences I.
6.
Att~
d . ~ . A c c a d . d . S c L F t s . Mat.
335
3 ( 2 7 ) , 1 (1868) G. Wyrouboff, BuII.Soc. Htn. F r a n c e S, 35 (1882) G. Wyrouboff, Bull.Soc. M~n. F r a n c e 13, 215 (1890) B.O. Hlldmann, PhD T h e s i s , TH Aachen (1980) P.E. Tomaszewskl, PhD Thesis, INTIBS PAN Wroct aw (1985) I.Sosnowska, B. Hilczer & P. Piskunowlcz, Soi~d State Commun. 74, 1249 (1990) A.R. Verma & P. Krlshna, polymorphLsm and potytyp(sm (n crystals, Wiley & Sons, New York (1966) A. Pletraszko & K.~.ukaszewicz, to be pub I ished. B.O. Hlldmann & Th. Hahn (1977), in: Powder D~ffraction F~le, No. 29-795 (1987) P. Brenner (1969), in: S.J.Chung: PhD Thesis, TH Aachen {1972}. J.Gllnnemann & Th. Hahn (1977), in: Powder D~ffructLon F£Le, No. 29-794 (1987) T. LIs (1980), private information A. Pletraszko & 3. St~ple~-Damm, private communication