No abstract

(6) and 2.541 (8) fi, for the Cu compound and for the Mn compound 2-300 (11) and 2.376 (12)/~. In-plane distances Cu-CI are 2.308 (2) and 2.896 (2) A and Mn-CI are 2.579 (3) and 2.600 (3) A: out of-plane distances are Cu-C1 = 2.316 (2) and Mn-CI = 2.508 (4) A.

No abstract

No abstract

The lattice parameters of ammonium chloride have been measured at 31.5 and 54"0°C. The coefficient of linear expansion is found to be 58-5 × 10-6°C -1.The thermal expansion of ammonium chloride (CsC1 structure) has been measured by Fizeau (1867) and Sharma (1950). The values reported by them for the coefficient of linear expansion near room temperature are 62.5 and 59"9 (in units of 10-6°C -I) respectively. HaussiJhl (1960) has quoted a very much lower value of 48 x 10-6°C -1. In view of these differences, an accurate X-ray determination of the coefficient of thermal expansion was undertaken.A flat-faced powder sample was prepared with Analar grade B.D.H. material. X-ray powder photographs were taken with a flat-film back-reflexion camera. With filtered copper radiation, the camera could record three ~:t2 doublets at high angles. Photographs were taken at 31.5 and at 54"0°C. The procedure for the precision determination of the lattice parameter was the same as in our earlier work * Present address: Physics Department, Post-graduate Centre, Warangal (A.P.), India. Acta Cryst. (1970). A26, 295A least-squares method for the determination of the orientation matrix in single-crystal ditfractometry.By K. TICHq,* Physics Department, University College, Cardiff', Wales (Received 6 October 1969) An appropriate choice of the function minimized permits linearization of the least-squares determination of the matrix which transforms the diffraction indices into the components of the reciprocal vector in the diffractometer ~0-axis system of coordinates. The coefficients of the least-squares equations are based on diffraction indices and measured diffractometer angles of three or more non-coplanar setting reflexions.