ANALYTICAL CHEMISTRY, VOL. 50, NO. 5, APRIL 1978 (189) Rao, C. N. R., Singh, S., Senthilnathan, V. P., Chem. SOC.Rev., 5, 297 (1976). (190) Rao, V. S.,Kalidas. C., Indian J , Chem., 13, 1303 (1975). (191) Rao, V. S., Kalidas. C., J . Chem. Eng. Data, 21, 314 (1976). (192) Remark, J. F., Reynolds, C. A., Talanta, 23, 687 (1976). (193) Robinson, E. H., “Proton Transfer Reactions”, Caldin, E., Gold, V., Ed., Chapman and Hall, London, 1975. (194) Rodehueser, L., Schneider, H., Z. Phys. Chem. (Frankfurl am Main), 100, 119 (1976). (195) Rondinini, S., Ardizzone, S.,Longhi, P..Mussini. T., Gazz. Chlm. Ita/., 106, 249 (1976). (196) Rosenfarb, J., Huffman, H. L., Caruso, J. A , , J . Chem. Eng. Data, 21, i.s-n -1isum ~ (197) Rosso, J. C., Carbonnel, L., C.R. Hebd. Seances Acad. Sci., Ser. C , 281, 955 (1975); Chem. Absfr., 84, 112361 (1976). (198) Ruzicka, E., Chem. Zvesti, 30, 160 (1976): Chem. Abstr., 87, 33293 (1977). (199) Saito. M., Kanamori, A., Bull. Chem. Soc. Jpn., 48, 3021 (1975). (200) Schaefer, 0. F., Ber. Bunsenges. Phys. Chem., 80, 529 (1976). (201) Schmid, R., Sapunov, V. N., Gutmann, V., 8er. Bunsenges. Phys. Chem., 80, 1302 (1976); Chem. Abstr., 86, 79379 (1977). (202) Schmid, R., Sapunov, V. N., Gutmann, V., 8 e r . Bunsenges. Phys. Chem., 80, 1307 (1976); Chem. Abstr., 86, 79380 (1977). (203) Schmidt, P. P., Electrochemistry, 5, 21 (1975). (204) Schneider, H., Top. Cur.. Chem., 68, 103 (1976). (205) Schneider, H., Electrochim. Acta. 21, 711 (1976). (206) Schuster, P., Electron-Solvent Anion-Solvent Interact., 259 (1976). (207) Schwartz, G. A., Barker, B. J., Talanta, 22, 773 (1975). (208) Sedivec, V., Flek, J., “Handbook of Analysis of Organic Solvents”, Ellis Horwood, Chichester, Engl., 1976. (209) Seiig. W., Mlcrochem. J . , 21, 291 (1976). (210) Shanmuganathan, S., Vivekanandan, S., Indian J . Chem., Sect. A , 15, 428 (1977). (211) Sharma, J. P.. Shukla, V. K. S., Dubey, A,, Mikrcchim. Acta, 1, 357 (1977). (212) Silber, H. E.. Pezzica, A.. J . Inorg. Nucl. Chem., 38, 2053 (1976). (213) Simmons, E. L., Prog. React. Kinet., 8, 161 (1977). (214) Smits, R., Massart, D. L., Juillard, J., Morel, J. P., Electrochim. Acta, 21, 425 (1976). (215) Smits. R.. Massart. D. L.. Juiliard. J.. Morel, J. P.. Electrochim. Acta. 21, 431 (1976). (216) Smits, R., Massart, D. L., Juillard, J , Morel, J. P., Electrochm Acta, 21 437 - 11976) ~-, (217) Solomatin, V. T., Rzhavichev. S. P., Zh. Anal. Khlm., 31, 2345 (1976); Chem. Abstr.. 87. 33168 11977). (218) Spitzer, U. A,, Toone, T. W., Siewart, R., Can. J . Ctiem., 54, 440 (1976). (219) Srivanavit, C., Zink, J. I . , Dechter, J. J., J , Am. Chem. Soc., 99, 5876 (1977). (220) Stock, J. T., Doane, L. M.,Anal. Chim. Acta, 86, 317 (1976).
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X-Ray Diffraction C. E. Pfluger Department of Chemistry, Syracuse University, Syracuse, New York 132 10
This review presents a general overview of the field of x-ray diffraction with emphasis being placed on the directions in which applications and research in the areas of instrumentation and the powder method have been going rather than attempting to present a comprehensive listing of all works in which x-ray diffraction was utilized. To do so would have been a formidable task indeed, as t h e use of x-ray diffraction in solving problems in chemistry, materials science, geology, industry, etc., is extremely wide-spread, as becomes obvious after even a rather superficial scan of the literature. This review covers the period from January 1976 through December 1977, mainly by the appearance of an abstract during this time, although several journals were independently scanned. I t is sincerely hoped t h a t no work of new and fundamental importance has been omitted. Books and reviews of a general nature which have appeared during the past two years include, a historical book by Bragg (20) tracing t h e development of x-ray analysis, a literature review of x-ray diffraction methods by DeVries (43),a review on t h e contribution of diffraction methods to the determination of chemical bonding, dynamics, and cooperative properties of crystalline materials by Bertaut ( I 3 ) ,and two volumes of t h e continuing series “Advances in X-Ray Analysis” which reports the proceedings of the highly regarded annual conference on the applications of x-ray analysis held 0003-2700/78/0350-161R$O 1.00/0
each August in Denver, Colo. (57, 102). T h e report of a conference held in February 1975 to consider the status and future potential of crystallography appeared in 1976 (112)in which it was concluded that the payoffs of crystallographic research have been and continue to be potentially large, not a surprising conclusion. Abrahams and Cohen ( I ) have also published a short review describing some of the recent developments in instrumental techniques which promise to significantly advance the role of crystallography in both applied and basic research.
INSTRUMENTATION As was mentioned in the previous review in ANALYTICAL CHEMISTRY (123),a symposium entitled “Instruments for Tomorrow’s Crystallography” was held a t the winter meeting of the American Crystallographic Association, January 19-23, 1976 (34),a t which time three emerging areas were considered to hold special promise: (1)the use of synchrotron radiation, (2) energy-dispersive diffractometry using solid-state detectors, and (3) the utilization of position-sensitive radiation detectors in x-ray diffraction instrumentation. There have been few developments during the recent past which have generated as much excitement and interest among researchers using both soft and hard x-radiation as t h e appearance on the scene of synchrotron radiation. Its extreme 0 1978 American Chemical Society
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intensity and “tunable” wavelength feature opens the door to many experiments which were previously not possible or were otherwise difficult to carry out. One of the most fruitful areas will undoubtedly be t h e study of dynamic processes, especially those occurring in exceptionally short time frames. Tanner (148) has recently reviewed the rapidly expanding field of study of dislocation dynamics and magnetic domain wall motion made possible by the enormous intensities of the synchrotron source. Other reviews have dealt with the DESY installation in Hamburg, Germany (83), the general characteristics and possible varied applications of the radiation (47),its application to structural studies (107, 118), and its application to high-temperature-high-pressure problems in geological systems (3). Some reported experiments involving the use of specially constructed instrumentation for synchrotron radiation and which demonstrate its potential are: cryogenic topography down to liquid nitrogen and liquid helium temperatures (149), energy-dispersive diffractometry of polycrystalline (18,22,23) or single-crystal materials (23), measurement of integrated diffraction intensities near an absorption edge (53, 125), small-angle scattering of soft (50 A) synchrotron radiation (136),and application of synchrotron radiation to protein crystallography (125). T h e field at present, however, may be likened to the “Model-T” age as experiments involving the use of a standard Precession camera (125),a modified slide projector to change films in a timeresolved topographic study (21),and a simple and inexpensive small-angle scattering camera (12) testify. I t is obvious that with the planned expansion of synchrotron sources (129), with construction costs being about 25 million dollars each and operating costs being of the order of 2.1 million dollars per year (129), a quantum jump in instrumental sophistication in the experimentation will be required in order t o take full advantage of t h e enormous increase in intensities and “tunability” features available from this source. Simply being able to slash exposure times by a factor of 10 or 100 is not sufficient justification for its use as the utilization of present technology in conventional high-intensity x-ray sources plus video tube or multiwire radiation detector systems allows one to carry out most of the experiments which have been reported to date a t a small fraction of t h e cost. I t is, of course, fully expected that the experimentation will eventually be more fully on a par with this exceptional light source. T h e recent report of a more sophisticated monochromator by Webb et al. (160) for small-angle studies is indicative of this trend. T h e rediscovery of energy-dispersive x-ray diffractometry has been prompted to some extent by the availability of the synchrotron source; however, it may also be said that the availability of lower cost electronics for lithium drifted silicon or intrinsic germanium detectors, made possible because of the enormous strides made by the electronics industry in the development and fabrication of integrated circuits, has also been a major contributing factor. A detailed discussion of the techniques of energy-dispersive x-ray diffractometry with semiconductor detectors has recently been given by Mantler (98) as well as reviews on the method have appeared both in the French (52) and Japanese (131)literature. Skelton (138) has reported on a simplified calibration procedure for energy-sensitive x-ray detectors. Energy-dispersive x-ray diffractometry is especially well suited to low- or high-temperature and/or high-pressure research (95. 145) as the instrumentation required can be considerably simplified and it is possible to follow dynamic changes in phases or structure with reasonable time resolution. Other applications of the method have been the measurement of lattice constants of two isotopes of molybdenum a t both room and low temperature which confirmed t h e isotopic volume effect in superconducting Mo (110),the measurement of the temperature dependence of Debye-Waller factors (137),the determination of the structure of thin amorphous films of tellurium on copper (96), and the measurement of the energy dependence of the Friedel pair intensities and their ratios near an absorption edge (54). Although few reports on multiwire proportional counter systems have appeared in the literature during the past two years, the potential of these devices should not be underestimated. Syntex Analytical Instruments, Inc. have recently unveiled their XID 2000 Electronic Powder Camera (146) which uses a multiwire proportional counter of semicylindrical geometry. Although the instrument is still in the develop-
mental stage, Syntex becomes the first company to offer an instrument incorporating this device. As expected, the speed of data gathering has been greatly enhanced. I t has been demonstrated that powder diffraction patterns from 0.2-mm diameter rotating powder specimens can be obtained in as little as 60 s using a normal sealed tube x-ray source. This may be compared to a powder pattern obtained using a synchrotron radiation source in 3 s (23);however, an irradiated sample volume approximately 20 times larger was used. Thus one notes that at the present stage of development of utilization of synchrotron radiation, improvements are not as dramatic as first assumed. Further reductions in exposure times on the multiwire device can be expected as further instrument development proceeds including, of course, the use of higher intensity x-ray sources such as rotating anode x-ray generators. The output of a multiwire detector contains information on both the time and position of the intercepted x-ray photon; thus, it becomes possible, by coupling the device to a computer, to do time-resolved x-ray diffractometry. Such an instrument has been constructed and the feasibility of the method demonstrated by Hashizume et al. (65). Their system has a time resolution of about 50 ~ s thus, ; it should prove to be useful for the study of dynamic events such as muscle contraction or other transient phenomena involving change of atomic, molecular, or crystal structure on a millisecond time scale. The usefulness of the multiwire proportional chamber as an area detector in single-crystal x-ray diffractometry, especially protein crystallography where a vast amount of data must be collected, was mentioned in the previous review (123). Forugi (51)has recently discussed this application in a detailed paper. T h e Ph.D. dissertation of Hamlin (631, who was intimately involved in the construction of a high-speed multiwire chamber-based data collection system for use in protein crystallography, has also appeared. Many reports of instrumentation for x-ray powder diffractometry have been concerned with the automation of both the diffractometer and the subsequent evaluation of the diffractometer output. Diano Corporation has recently made available a semiautomatic powder diffractometer with micro processor control (44). Holland and Medrud (70) have reported on their computer-controlled automatic powder diffractometer of some flexibility which includes an automatic sample changer and computer subroutines for sample phase identification. Several groups have reported on their application of minicomputer search systems for phase identification from powder x-ray diffraction data (24, 60, 114, 11 9). The usefulness of a completely automated system for many industrial applications is obvious. One of the original workers in the field of computerization of identification of x-ray powder patterns, G. G. Johnson, Jr., has recently published an extensive review of the subject ( 7 5 ) . Single-crystal x-ray diffractometers were among the first laboratory instruments to be automated. Computer-controlled single-crystal diffractometers are now found in very many crystallographic laboratories. Sparks (143) has recently reviewed the applications of computers, usually minicomputers, in single-crystal diffractometry. Other reports on single-crystal instrumentation include: the coupling of a rotating anode x-ray source to a 4-circle single-crystal diffractometer (100); the equipping of a 4-circle single-crystal diffractometer with an interchangeable Si(Li) solid-state detector (58); a new method for simultaneous photography of two lattice planes of reciprocal lattices by a method which combines the advantages of both the precession and the deJong-Bouman methods (74);a method of photographing the reciprocal lattice with the axis of the film cylinder intersecting the rotation axis of the crystal at 45’ (28);the use of convergent beams of x-rays to obtain pseudo-rotation diffraction patterns from protein crystals (166);and a review of the collimation and monochromatization techniques used in the rotation method ( 7 ) . The application of a curved graphite crystal monochromator to x-ray diffractometry has been reported on by McRae and Waggoner (103) and a very simple monochromator design employing a flat graphite crystal has been described by Denne (42). In the quest for increased x-ray source intensities, the common sealed x-ray tube has not been completely neglected. Philips Industries (124) has announced a new generation of x-ray tubes in which power ratings have been significantly improved (25-3570 for Cu and 35-6770 for Mo) by improved
ANALYTICAL CHEMISTRY, VOL. 50, NO. 5, APRIL 1978 C. E. Pfluger is professor of chemistry at Syracuse University, Syracuse, N.Y., where he has been since 1967. He received his B.S. degree from the University of Texas in 1951 and after a three-year period of employment by the atomic energy division of Du Pont, began graduate work at the University of Texas, receiving his Ph.D. in 1958. After a postdoctoral year at the Technical University at Darmstadt, Germany, on a Fulbright grant, he joined the analytical chemistry faculty of the University of Illinois where he remained until 1965. He was a Fulbright Lecturer at Denmark's Technical University in Copenhagen during the 1965-1966 academic year and assistant professor of chemistry at the Univers research has dealt primarily with the determination of crystal and molecular structure by single crystal x-ray diffraction techniques.
anode cooling. In addition, the spectral purity characteristics have been improved by a new tube geometry and lower filament currents. X-ray diffraction studies in the nanosecond range, for example investigation of solids undergoing shock compression, have used flash x-ray generators. Japanese (85)and Russian ( 8 ) workers have reported on their systems for extremely high-speed x-ray diffraction studies. Also of interest and of great potential usefulness is the report of Green (59) on a portable flash x-ray system with which he has obtained Laue transmission x-ray diffraction patterns with exposure times as short as several microseconds. In surveying the literature, one cannot help but be struck by the enormous amount of research effort going on in the field which is generally called "materials science". It is clear that an understanding of the properties of the solid state can only be obtained by a detailed knowledge of the solid state (defects, structure, etc.) a t varied temperature and pressure. It is thus not surprising to see a rather large number of reports concerned with instrumentation for low-temperature, hightemperature, high-pressure, topographic, and thin film studies. In the low-temperature field, a very comprehensive book on apparatus and techniques has been written by Rudman (130). Two reports (93, 115) on cryostats suitable for use down to essentially liquid helium temperature have appeared along with two reports of gas flow systems for automatic singlecrystal diffractometry down t o liquid nitrogen temperature (32, 40). Lippman and Rudman (92) have investigated the use of mechanically refrigerated units to cool gas streams to about -120 "C and a specially constructed 0-0 diffractometer for t h e study of liquids and glassy materials a t very low temperatures has been described by Bizid et al. (15). In the high-temperature field, a review by Viswamitra (255) on high-temperature single-crystal diffraction methods has appeared. Reports on high-temperature instrumentation include: an automatically recording high-temperature Laue camera (127);a powder diffractometer furnace capable of reaching 1700 "C using a thermal imaging technique (159); a new precession camera furnace (104);and a high-temperature x-ray topography system which allows in-situ investigation of temperature induced defect generation, multiplication, and movement in semiconductor single crystals (66). Two variable temperature systems have also been described specifically for the investigation of liquid crystal phases (29, 32). In the high-pressure field, all instrumentation reports have dealt with some aspect of the diamond anvil high-pressure cell. Hasegawa et al. (64)have reported on the use of a rotating target x-ray source for high-pressure and high-temperature studies; Skelton et al. (239)have described a versatile cell which can be used down to 2 K; high-pressure cells suitable for use on single-crystal cameras and diffractometers were described by Schiferl (132) and Keller and Holzapfel (80); modifications of the cell which allows measurement of strains and strengths of materials u p to 300 kbars were reported by Kinsland and Bassett (81);and the use of fine-grained diamond particles mixed with epoxy resin t o form a pressure cell for x-ray diffraction has been described by Kawai et al. (78). An instrument assuming ever-increasing importance in the study of perfection of real crystals is the multiple-crystal diffractometer. T h e construction and testing of a simple
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double-crystal diffractometer has been described by Daenhardt (39), while Russian workers have reported on the construction of a 3-crystal device (87). T h e development of a computer controlled triple-crystal x-ray diffractometer by Pick e t al. (226)is clearly the most significant work reported in this field during the past two years. This device is able to automatically make intensity measurements in any direction in reciprocal space in the diffracting plane with step sizes down to 0.01 inch of arc. Some of its many uses include the characterization of the perfection of crystals and a study of diffuse scattering close to the Bragg peak from defect clusters in irradiated almost perfect single crystals. Other reports of instruments for materials science investigations include: a Lang camera for large-scale x-ray transmission topography (90);a Russian report of a flat and cylindrical cassette topographic camera (10);an asymmetric crystal topographic camera (17);a camera for divergent beam diagrams (88);two T V systems for the direct viewing of x-ray topographs of defects (24, 242); a convergent beam camera for the x-ray diffraction study of whiskers
