International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

© International Union of Crystallography 2006
International Tables for Crystallography (2006). Vol. C. ch. 5.3, p. 510

Section 5.3.2.3.5. Photographic cameras for investigation of small lattice-parameter changes

E. Gałdeckaa

a Institute of Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 937, 50-950 Wrocław 2, Poland

5.3.2.3.5. Photographic cameras for investigation of small lattice-parameter changes

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Small changes of lattice parameters caused by thermal expansion or other factors can be investigated in multiple-exposure cameras.

Bearden & Henins (1965[link]) used the double-crystal spectrometer with photographic detection to examine imperfections and stresses of large crystals. The technique allowed the detection of angle deviations as small as 0.5′′. A nearly perfect calcite crystal was used as the first crystal (monochromator), the sample was the second. The device distinguished itself with very good sensitivity. The use of the long distance (200 cm) between the focus and the second crystal made possible resolution of the doublet [K\alpha_{1,2}], and elimination of the [K\alpha_2] radiation. An additional advantage was that the arrangement was less time-consuming, so that it was suitable for controlling the perfection of growing crystals and useful for choosing adequate samples for the wavelength measurements.

Kobayashi, Yamada & Azumi (1968[link]) have described a special `strainmeter' for measuring small strains of the lattice. The strain [x_i] along an axis normal to the i plane results in a change [\delta d_i] of the interplanar distance [d_i]: [x_i=\delta d_i/d_i=-\cot\theta_i\delta_i. \eqno (5.3.2.5)]The use of a large camera radius R = 2639 mm makes it possible to obtain both high sensitivity and high precision (2 parts in 106) even in the range of lower Bragg angles [(\theta\simeq55^\circ)]. The device is suitable for the investigation of defects resulting from small strains and may be used in measurements of thermal expansion.

Glazer (1972[link]) described an automatic arrangement, based on the Weissenberg goniometer, for the photographic recording of high-angle Bragg reflections as a function of temperature, pressure, time, etc. A careful choice of the oscillation axis and oscillation range makes it possible to obtain a distorted but recognizable phase diagram (Fig. 5.3.2.1[link] ) within several hours. The method had been applied by Glazer & Megaw (1973[link]) in studies of the phase transitions of NaNbO3.

[Figure 5.3.2.1]

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(a) Photographic recording of lattice-parameter changes. (b) Corresponding diagram of the variation of lattice parameters in pseudocubic NaNbO3 (Glazer & Megaw, 1973[link]).

Popović, Šljukić & Hanic (1974[link]) used a Weissenberg camera equipped with a thermocouple mounted on the goniometer head for precise measurement of lattice parameters and thermal expansion in the high-temperature range.

References

First citation Bearden, J. A. & Henins, A. (1965). Precision measurement of lattice imperfections with a photographic two-crystal method. Rev. Sci. Instrum. 36, 334–338.Google Scholar
 First citation Glazer, A. M. (1972). A technique for the automatic recording of phase transitions in single crystals. J. Appl. Cryst. 5, 420–423.Google Scholar
 First citation Glazer, A. M. & Megaw, H. D. (1973). Studies of the lattice parameters and domains in the phase transitions of NaNbO3. Acta Cryst. A29, 489–495.Google Scholar
 First citation Kobayashi, J., Yamada, N. & Azumi, I. (1968). An X-ray method for accurate determination of lattice strain of crystals. Rev. Sci. Instrum. 39, 1647–1650.Google Scholar
 First citation Popović, S., Šljukić, M. & Hanic, F. (1974). Precise unit cell parameter and thermal expansion measurements of single crystals by X-ray diffraction. Phys. Status Solidi A, 23, 265–274.Google Scholar








































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