- Email: [email protected]
Analysis of some aspects of synchrotron radiation measurements reported in the inorganic crystal structure database
Journal of Alloys and Compounds 286 (1999) 219–223
L
Analysis of some aspects of synchrotron radiation measurements reported in the inorganic crystal structure database Jerzy Andrzej Sokol«owski ´ , Poland Faculty of Chemistry, Jagiellonian University, ul. Ingardena 3, 30 -060 Krakow
Abstract The Inorganic Crystal Structure Database (Gmelin Institut, Fachinformationszentrum Karlsruhe, Release 97 / 2) contains over 45 000 structures collected, from the year 1915 up to now. Among them, 191 structures have been solved or refined on the basis of data collected with synchrotron radiation. The distribution of the number of structures as a function of year, atomic number, unit cell volume, and number of types of elements in the studied compounds was investigated. The study included data from synchrotron powder diffraction, neutron powder diffraction, X-ray powder diffraction and up to four other techniques. 1999 Elsevier Science S.A. All rights reserved. Keywords: Frequency of occurrence of structures; Synchrotron radiation application; Neutron diffraction; X-ray powder diffraction
1. Introduction Easy access to structural data from databases enables an analysis of the number of structures registered over the years. The Inorganic Crystal Structure Database (ICSD) [1] contains data of 45 914 records (including 2843 structures calculated theoretically), registered for the years 1915–1997. There is about a half year delay in the data registration and the data for a few of the last years are incomplete. In this set of data, only 191 structures are determined with the use of synchrotron radiation. Such a low number of structures (less than 0.5% of the total) shows that the techniques using synchrotron radiation are rather young in the field of inorganic compounds.
2. Results and discussion The list of journals, in which the data registered in the ICSD database are published, is given in Table 1. For each of the considered techniques of measurements the journals are arranged according to the decreasing number of structures published in them. It can be noticed that in the case of synchrotron radiation powder diffraction the preferred journals are those concerning physical properties and the basic features of compounds. Then follows the journals that focus on zeolites and minerals. E-mail address: [email protected] (J.A. Sokol«owski)
The histograms showing the number of structures for which ICSD data were collected using seven different diffraction techniques are presented in Fig. 1. These techniques are: X-ray powder diffraction (XRPD), neutron powder diffraction (NPD), synchrotron radiation powder diffraction (SRPD), synchrotron radiation single crystal diffraction (SRSCD), electron single crystal diffraction (ESCD), electron powder diffraction (EPD) and neutron single crystal diffraction (NSCD). The X-ray single crystal technique is not indicated as a different category in the database and therefore does not appear as a separate entry in Fig. 1. It can be seen that the use of neutron powder diffraction follows an exponential growth. The fitted function [5.451exp((year21949.4(3))30.1430(3))] accounts for 99.1% of the variability of the number of structures yearly in the time range from 1948 (first record) to 1994 (from 1995 the data are incomplete). The use of X-ray powder diffraction gives a very similar number of structures (Table 2) and is exponentially growing as well, but in the middle of the 1960s a short period of stagnation can be noticed. The fitted function presented in Fig. 1 (the number of records yearly579(7)1exp((year21976.1(9))3 0.35(2)), variance explained 95.13%) was calculated using data from 1962. Taking into consideration earlier data means that the function accounts for less than 95% of the variability. Other functions with three parameters gave purer results. The database contains only 149 structures measured with the use of synchrotron powder diffraction. The first
0925-8388 / 99 / $ – see front matter 1999 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 98 )01010-X
220
J. A. Sokol«owski / Journal of Alloys and Compounds 286 (1999) 219 – 223
Table 1 The list of journals, in which the data registered in the ICSD database are published Frequency
Fraction (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Synchrotron radiation powder diffractometry Physical Review, Series 3, B, Condensed Matter Journal of Applied Crystallography Acta Crystallographica C Zeolites Journal of Solid State Chemistry Acta Crystallographica B Journal of Physics and Chemistry of Solids American Mineralogist European Journal of Solid State Inorganic Chemistry Fortschritte der Mineralogie Acta Crystallographica Acta Crystallographica A European Journal of Mineralogy Neues Jahrbuch fuer Mineralogie, Abhandlungen
28 18 9 9 7 6 6 5 5 5 4 4 4 4
18.30 11.76 5.88 5.88 4.58 3.92 3.92 3.27 3.27 3.27 2.61 2.61 2.61 2.61
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Neutron powder diffraction Journal of Solid State Chemistry Physica C Acta Crystallographica B Journal of Alloys and Compounds Physical Review, Series 3, B, Condensed Matter Materials Research Bulletin Journal of Physics: Condensed Matter Solid State Communications Journal of the Less-Common Metals Zeitschrift fuer Anorganische und Allgemeine Chemie Zeitschrift fuer Kristallographie Solid State Ionics Acta Chemica Scandinavica, Series A Acta Crystallographica C
894 552 390 315 262 232 196 182 144 132 120 99 91 89
16.52 10.20 7.20 5.82 4.84 4.29 3.62 3.36 2.66 2.44 2.22 1.83 1.68 1.64
1 2 3 4 5 6 7 8 9 10 11 12 13 14
X-ray powder diffraction Journal of Solid State Chemistry Zeitschrift fuer Anorganische und Allgemeine Chemie Materials Research Bulletin Physica C Zeitschrift fuer Kristallographie Acta Crystallographica Journal of the American Chemical Society Journal of the Less-Common Metals Zeitschrift fuer Naturforschung, Teil B, Anorganische Chemie Acta Crystallographica B Journal of Alloys and Compounds Inorganic Chemistry American Mineralogist Journal of Physical Chemistry
788 570 331 237 206 184 144 141 137 136 133 130 108 101
12.22 8.84 5.13 3.67 3.19 2.85 2.23 2.19 2.12 2.11 2.06 2.02 1.67 1.57
data are from the year 1981. It is difficult to predict whether the points on that histogram will follow the exponential or slow linear growth (as in the cases of NSCD, EPD and ESCD (Fig. 1)), because the statistics are too poor. In ICSD database there are 42 structures determined using the synchrotron radiation single crystal technique. The histogram of this data is very similar to that of synchrotron powder diffraction; however, any prediction is even more difficult as the number of records is smaller. Assuming that all the diffraction methods considered here are equally accessible, the choice of the type of
radiation should be determined mainly by the kind of elements present in the studied samples. Fig. 2 shows the distribution of structures, refined or solved on the basis of measurements done with the specified technique, over the elements, with Z in the range from 1 to 91. In all the analyzed methods (XPD, NPD and SRPD) for which the distribution diagrams are given in Fig. 2, the most intensive maxima correspond to oxygen. Surprisingly, in the NPD and XPD methods the second highest peak corresponds to copper. The weaker maxima occur for barium, strontium and bismuth, these being present together with copper in high-temperature superconductors, indicating
J. A. Sokol«owski / Journal of Alloys and Compounds 286 (1999) 219 – 223
Fig. 1. The number of structures collected in the ICSD database as a function of the year. Abbreviations: XRPD (X-ray powder diffraction), NPD (neutron powder diffraction), SRPD (synchrotron radiation powder diffraction), SRSCD (synchrotron radiation single crystal diffraction), ESCD (electron single crystal diffraction), EPD (electron powder diffraction) and NSCD (neutron single crystal diffraction) (used throughout).
that the peak of copper comes mainly from this group of compounds. These maxima are very weak for the synchrotron radiation technique. In the case of the SRPD method the second highest peak comes from silicon and is connected with zeolites. In all three techniques the structures of the compounds containing hydrogen are common and, as might be expected, the maximum is highest for structures determined with the neutron powder diffraction. Despite some differences, the three distributions shown in Fig. 2 are similar—maxima and minima are in the same positions, relative intensities do not differ very much between different measurement methods, especially for the less intensive peaks. These similarities resulted in high correlation factors between the distributions (Table 3).
221
Fig. 2. The distribution of structures over elements. The x-axis follows the atomic number. Table 3 The correlation factors between distributions of structures over elements XRPD, NPD and synchrotron radiation powder diffraction (SRPD)
%XRPD %NPD %SRPD
%XRPD
%NPD
%SRPD
1.00 0.81 0.93
0.81 1.00 0.67
0.93 0.67 1.00
It can be noticed that the correlation between the distributions for neutron powder diffraction and X-ray powder diffraction (0.81) is higher than the correlation between neutron powder diffraction and synchrotron radiation powder diffraction (0.67). It is surprising because: (a) the application of the classical X-ray radiation is much more limited than synchrotron radiation, which is less specific for the composition of elements in the samples; (b)
Table 2 The number of structures determined using different methods and the fraction of structures for which measurements were carried out under defined temperature or non-ambient pressure conditions
Number of structures Defined temperature Fraction of all structures (%) Non-ambient pressure Fraction of all structures (%)
SRSCD
SRPD
NSCD
NPD
XRPD
42 6 14.29 7 16.67
149 33 22.15 36 24.16
1012 461 45.55 16 1.58
5292 2884 54.50 144 2.72
6356 685 10.78 38 0.60
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J. A. Sokol«owski / Journal of Alloys and Compounds 286 (1999) 219 – 223
scattering lengths for the neutron methods are different than for X-ray techniques. It follows that the correlation between the distribution of the elements in the samples measured with neutron powder diffraction and the synchrotron powder diffraction techniques should be higher. The reason for that lies in the fact that the access to the synchrotron radiation is still somewhat limited. It results in more careful choice of samples measured with that method. To compare the size of the structures measured with different techniques, the unit cell volume seems to be a useful descriptor. The median and the average of that quantity is slowly growing over the years (Table 4). For the synchrotron radiation powder diffraction technique the ˚ 3 ) and the average is median is rather low (389.2 A 3 ˚ ). The value of the latter is relatively high (1036.9 A affected by the second maximum present on the histogram ˚ 3 (Fig. 3). This of the unit cell volumes at about 2600 A maximum comes from zeolites. It seems that up to now zeolites were one of the compounds most intensively investigated using synchrotron radiation. The clue to the explanation of the small volume corresponding to the first maximum in the histogram of SRPD in Fig. 3 is the distribution of structures over the number of elements in the compounds (Fig. 4). In comparison with the other techniques, a very big fraction of the structures determined using synchrotron powder diffraction includes only one or two elements. These compounds have usually a small unit cell volume, and are responsible for the first maximum in Fig. 3. It can be expected that investigations of simple compounds were done under varying temperature or / and pressure conditions. The comparison of the usage of the controlled temperature and controlled pressure in different diffraction techniques is given in Table 2. The fraction of structures determined under controlled temperature is, in the case of the synchrotron radiation powder technique, twice as high as that for the X-ray powder diffraction, but at the same time it is twice as low as for the case of neutron powder diffraction. In the case of controlled pressure the synchrotron radiation techniques seem to be unbeatable –the fraction of structures determined under controlled pressure is one order higher for these methods. Synchrotron radiation diffraction allows us to establish the occupancy factor of many elements, substituting simul-
Fig. 3. The distribution of the unit cell volume of the structures from the ICSD database. The dashed line shows all the structures registered after 1990, and the continuous line shows only the structures determined using the synchrotron radiation powder technique.
Fig. 4. The number of structures of the compounds as a function of the number of types of elements in the compound.
Table 4 The average and median of unit cells volume for different methods, and the fraction of the structures for which no R value was given in the papers Structures from ICSD from the years
Average unit cell volume Median of unit cell volume Fraction of structures for which no R value was given in the references (%)
1915–1970
1990–1997
733.1 406.7 60.2
986.2 526.1 5.5
SRPD
SRSCD
XRPD
NPD
NSCD
EPD
ESCD
1036.9 389.2 21.5
503.2 411.3 11.9
725.1 368.3 38.9
551.0 301.5 12.7
668.8 443.6 6.7
709.9 448.6 40.30
836.4 333.6 47.1
J. A. Sokol«owski / Journal of Alloys and Compounds 286 (1999) 219 – 223
taneously the same positions. This option is very useful in the investigation of minerals. In the ICSD database 17% of the structures determined using the synchrotron powder diffraction technique are minerals. Among them are natural and synthetic minerals. The fraction of minerals studied using X-ray powder diffraction is 12% and using neutron powder diffraction it is only 6%.
3. Conclusions The analysis of the Inorganic Crystal Structure Database shows that in the field of inorganic compounds the synchrotron radiation diffraction techniques are applied mainly only to these three categories of compounds: zeolites, minerals and compounds containing only one or two elements. The number of structures determined using the techniques is small. This suggests that access to synchrotron radiation is strongly limited. When the access becomes easier the scope of the methods may rapidly broaden, as was the case with the Rietveld method [2,3],
223
which started to expand rapidly 20 years after its invention, when personal computers where introduced.
Acknowledgements The author is grateful to Dr. Maria Ciechanowicz-Rutkowska from the Regional Laboratory for Physicochemical ´ and Dr. Analyses and Structural Research in Krakow Wojciech Paszkowicz from the Institute of Physics, Polish Academy of Sciences in Warsaw for fruitful discussions and editorial help.
References [1] Inorganic Crystal Structure Database, Gmelin Institut, Fachinformationszentrum Karlsruhe, Release 97 / 2. [2] H.M. Rietveld, Acta Cryst. 22 (1967) 151. [3] H.M. Rietveld, J. Appl. Cryst. 2 (1969) 65.
L
Analysis of some aspects of synchrotron radiation measurements reported in the inorganic crystal structure database Jerzy Andrzej Sokol«owski ´ , Poland Faculty of Chemistry, Jagiellonian University, ul. Ingardena 3, 30 -060 Krakow
Abstract The Inorganic Crystal Structure Database (Gmelin Institut, Fachinformationszentrum Karlsruhe, Release 97 / 2) contains over 45 000 structures collected, from the year 1915 up to now. Among them, 191 structures have been solved or refined on the basis of data collected with synchrotron radiation. The distribution of the number of structures as a function of year, atomic number, unit cell volume, and number of types of elements in the studied compounds was investigated. The study included data from synchrotron powder diffraction, neutron powder diffraction, X-ray powder diffraction and up to four other techniques. 1999 Elsevier Science S.A. All rights reserved. Keywords: Frequency of occurrence of structures; Synchrotron radiation application; Neutron diffraction; X-ray powder diffraction
1. Introduction Easy access to structural data from databases enables an analysis of the number of structures registered over the years. The Inorganic Crystal Structure Database (ICSD) [1] contains data of 45 914 records (including 2843 structures calculated theoretically), registered for the years 1915–1997. There is about a half year delay in the data registration and the data for a few of the last years are incomplete. In this set of data, only 191 structures are determined with the use of synchrotron radiation. Such a low number of structures (less than 0.5% of the total) shows that the techniques using synchrotron radiation are rather young in the field of inorganic compounds.
2. Results and discussion The list of journals, in which the data registered in the ICSD database are published, is given in Table 1. For each of the considered techniques of measurements the journals are arranged according to the decreasing number of structures published in them. It can be noticed that in the case of synchrotron radiation powder diffraction the preferred journals are those concerning physical properties and the basic features of compounds. Then follows the journals that focus on zeolites and minerals. E-mail address: [email protected] (J.A. Sokol«owski)
The histograms showing the number of structures for which ICSD data were collected using seven different diffraction techniques are presented in Fig. 1. These techniques are: X-ray powder diffraction (XRPD), neutron powder diffraction (NPD), synchrotron radiation powder diffraction (SRPD), synchrotron radiation single crystal diffraction (SRSCD), electron single crystal diffraction (ESCD), electron powder diffraction (EPD) and neutron single crystal diffraction (NSCD). The X-ray single crystal technique is not indicated as a different category in the database and therefore does not appear as a separate entry in Fig. 1. It can be seen that the use of neutron powder diffraction follows an exponential growth. The fitted function [5.451exp((year21949.4(3))30.1430(3))] accounts for 99.1% of the variability of the number of structures yearly in the time range from 1948 (first record) to 1994 (from 1995 the data are incomplete). The use of X-ray powder diffraction gives a very similar number of structures (Table 2) and is exponentially growing as well, but in the middle of the 1960s a short period of stagnation can be noticed. The fitted function presented in Fig. 1 (the number of records yearly579(7)1exp((year21976.1(9))3 0.35(2)), variance explained 95.13%) was calculated using data from 1962. Taking into consideration earlier data means that the function accounts for less than 95% of the variability. Other functions with three parameters gave purer results. The database contains only 149 structures measured with the use of synchrotron powder diffraction. The first
0925-8388 / 99 / $ – see front matter 1999 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 98 )01010-X
220
J. A. Sokol«owski / Journal of Alloys and Compounds 286 (1999) 219 – 223
Table 1 The list of journals, in which the data registered in the ICSD database are published Frequency
Fraction (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Synchrotron radiation powder diffractometry Physical Review, Series 3, B, Condensed Matter Journal of Applied Crystallography Acta Crystallographica C Zeolites Journal of Solid State Chemistry Acta Crystallographica B Journal of Physics and Chemistry of Solids American Mineralogist European Journal of Solid State Inorganic Chemistry Fortschritte der Mineralogie Acta Crystallographica Acta Crystallographica A European Journal of Mineralogy Neues Jahrbuch fuer Mineralogie, Abhandlungen
28 18 9 9 7 6 6 5 5 5 4 4 4 4
18.30 11.76 5.88 5.88 4.58 3.92 3.92 3.27 3.27 3.27 2.61 2.61 2.61 2.61
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Neutron powder diffraction Journal of Solid State Chemistry Physica C Acta Crystallographica B Journal of Alloys and Compounds Physical Review, Series 3, B, Condensed Matter Materials Research Bulletin Journal of Physics: Condensed Matter Solid State Communications Journal of the Less-Common Metals Zeitschrift fuer Anorganische und Allgemeine Chemie Zeitschrift fuer Kristallographie Solid State Ionics Acta Chemica Scandinavica, Series A Acta Crystallographica C
894 552 390 315 262 232 196 182 144 132 120 99 91 89
16.52 10.20 7.20 5.82 4.84 4.29 3.62 3.36 2.66 2.44 2.22 1.83 1.68 1.64
1 2 3 4 5 6 7 8 9 10 11 12 13 14
X-ray powder diffraction Journal of Solid State Chemistry Zeitschrift fuer Anorganische und Allgemeine Chemie Materials Research Bulletin Physica C Zeitschrift fuer Kristallographie Acta Crystallographica Journal of the American Chemical Society Journal of the Less-Common Metals Zeitschrift fuer Naturforschung, Teil B, Anorganische Chemie Acta Crystallographica B Journal of Alloys and Compounds Inorganic Chemistry American Mineralogist Journal of Physical Chemistry
788 570 331 237 206 184 144 141 137 136 133 130 108 101
12.22 8.84 5.13 3.67 3.19 2.85 2.23 2.19 2.12 2.11 2.06 2.02 1.67 1.57
data are from the year 1981. It is difficult to predict whether the points on that histogram will follow the exponential or slow linear growth (as in the cases of NSCD, EPD and ESCD (Fig. 1)), because the statistics are too poor. In ICSD database there are 42 structures determined using the synchrotron radiation single crystal technique. The histogram of this data is very similar to that of synchrotron powder diffraction; however, any prediction is even more difficult as the number of records is smaller. Assuming that all the diffraction methods considered here are equally accessible, the choice of the type of
radiation should be determined mainly by the kind of elements present in the studied samples. Fig. 2 shows the distribution of structures, refined or solved on the basis of measurements done with the specified technique, over the elements, with Z in the range from 1 to 91. In all the analyzed methods (XPD, NPD and SRPD) for which the distribution diagrams are given in Fig. 2, the most intensive maxima correspond to oxygen. Surprisingly, in the NPD and XPD methods the second highest peak corresponds to copper. The weaker maxima occur for barium, strontium and bismuth, these being present together with copper in high-temperature superconductors, indicating
J. A. Sokol«owski / Journal of Alloys and Compounds 286 (1999) 219 – 223
Fig. 1. The number of structures collected in the ICSD database as a function of the year. Abbreviations: XRPD (X-ray powder diffraction), NPD (neutron powder diffraction), SRPD (synchrotron radiation powder diffraction), SRSCD (synchrotron radiation single crystal diffraction), ESCD (electron single crystal diffraction), EPD (electron powder diffraction) and NSCD (neutron single crystal diffraction) (used throughout).
that the peak of copper comes mainly from this group of compounds. These maxima are very weak for the synchrotron radiation technique. In the case of the SRPD method the second highest peak comes from silicon and is connected with zeolites. In all three techniques the structures of the compounds containing hydrogen are common and, as might be expected, the maximum is highest for structures determined with the neutron powder diffraction. Despite some differences, the three distributions shown in Fig. 2 are similar—maxima and minima are in the same positions, relative intensities do not differ very much between different measurement methods, especially for the less intensive peaks. These similarities resulted in high correlation factors between the distributions (Table 3).
221
Fig. 2. The distribution of structures over elements. The x-axis follows the atomic number. Table 3 The correlation factors between distributions of structures over elements XRPD, NPD and synchrotron radiation powder diffraction (SRPD)
%XRPD %NPD %SRPD
%XRPD
%NPD
%SRPD
1.00 0.81 0.93
0.81 1.00 0.67
0.93 0.67 1.00
It can be noticed that the correlation between the distributions for neutron powder diffraction and X-ray powder diffraction (0.81) is higher than the correlation between neutron powder diffraction and synchrotron radiation powder diffraction (0.67). It is surprising because: (a) the application of the classical X-ray radiation is much more limited than synchrotron radiation, which is less specific for the composition of elements in the samples; (b)
Table 2 The number of structures determined using different methods and the fraction of structures for which measurements were carried out under defined temperature or non-ambient pressure conditions
Number of structures Defined temperature Fraction of all structures (%) Non-ambient pressure Fraction of all structures (%)
SRSCD
SRPD
NSCD
NPD
XRPD
42 6 14.29 7 16.67
149 33 22.15 36 24.16
1012 461 45.55 16 1.58
5292 2884 54.50 144 2.72
6356 685 10.78 38 0.60
222
J. A. Sokol«owski / Journal of Alloys and Compounds 286 (1999) 219 – 223
scattering lengths for the neutron methods are different than for X-ray techniques. It follows that the correlation between the distribution of the elements in the samples measured with neutron powder diffraction and the synchrotron powder diffraction techniques should be higher. The reason for that lies in the fact that the access to the synchrotron radiation is still somewhat limited. It results in more careful choice of samples measured with that method. To compare the size of the structures measured with different techniques, the unit cell volume seems to be a useful descriptor. The median and the average of that quantity is slowly growing over the years (Table 4). For the synchrotron radiation powder diffraction technique the ˚ 3 ) and the average is median is rather low (389.2 A 3 ˚ ). The value of the latter is relatively high (1036.9 A affected by the second maximum present on the histogram ˚ 3 (Fig. 3). This of the unit cell volumes at about 2600 A maximum comes from zeolites. It seems that up to now zeolites were one of the compounds most intensively investigated using synchrotron radiation. The clue to the explanation of the small volume corresponding to the first maximum in the histogram of SRPD in Fig. 3 is the distribution of structures over the number of elements in the compounds (Fig. 4). In comparison with the other techniques, a very big fraction of the structures determined using synchrotron powder diffraction includes only one or two elements. These compounds have usually a small unit cell volume, and are responsible for the first maximum in Fig. 3. It can be expected that investigations of simple compounds were done under varying temperature or / and pressure conditions. The comparison of the usage of the controlled temperature and controlled pressure in different diffraction techniques is given in Table 2. The fraction of structures determined under controlled temperature is, in the case of the synchrotron radiation powder technique, twice as high as that for the X-ray powder diffraction, but at the same time it is twice as low as for the case of neutron powder diffraction. In the case of controlled pressure the synchrotron radiation techniques seem to be unbeatable –the fraction of structures determined under controlled pressure is one order higher for these methods. Synchrotron radiation diffraction allows us to establish the occupancy factor of many elements, substituting simul-
Fig. 3. The distribution of the unit cell volume of the structures from the ICSD database. The dashed line shows all the structures registered after 1990, and the continuous line shows only the structures determined using the synchrotron radiation powder technique.
Fig. 4. The number of structures of the compounds as a function of the number of types of elements in the compound.
Table 4 The average and median of unit cells volume for different methods, and the fraction of the structures for which no R value was given in the papers Structures from ICSD from the years
Average unit cell volume Median of unit cell volume Fraction of structures for which no R value was given in the references (%)
1915–1970
1990–1997
733.1 406.7 60.2
986.2 526.1 5.5
SRPD
SRSCD
XRPD
NPD
NSCD
EPD
ESCD
1036.9 389.2 21.5
503.2 411.3 11.9
725.1 368.3 38.9
551.0 301.5 12.7
668.8 443.6 6.7
709.9 448.6 40.30
836.4 333.6 47.1
J. A. Sokol«owski / Journal of Alloys and Compounds 286 (1999) 219 – 223
taneously the same positions. This option is very useful in the investigation of minerals. In the ICSD database 17% of the structures determined using the synchrotron powder diffraction technique are minerals. Among them are natural and synthetic minerals. The fraction of minerals studied using X-ray powder diffraction is 12% and using neutron powder diffraction it is only 6%.
3. Conclusions The analysis of the Inorganic Crystal Structure Database shows that in the field of inorganic compounds the synchrotron radiation diffraction techniques are applied mainly only to these three categories of compounds: zeolites, minerals and compounds containing only one or two elements. The number of structures determined using the techniques is small. This suggests that access to synchrotron radiation is strongly limited. When the access becomes easier the scope of the methods may rapidly broaden, as was the case with the Rietveld method [2,3],
223
which started to expand rapidly 20 years after its invention, when personal computers where introduced.
Acknowledgements The author is grateful to Dr. Maria Ciechanowicz-Rutkowska from the Regional Laboratory for Physicochemical ´ and Dr. Analyses and Structural Research in Krakow Wojciech Paszkowicz from the Institute of Physics, Polish Academy of Sciences in Warsaw for fruitful discussions and editorial help.
References [1] Inorganic Crystal Structure Database, Gmelin Institut, Fachinformationszentrum Karlsruhe, Release 97 / 2. [2] H.M. Rietveld, Acta Cryst. 22 (1967) 151. [3] H.M. Rietveld, J. Appl. Cryst. 2 (1969) 65.