Forgot Password | New Account

High-resolution two-axis diffractometer D1A

The high-resolution powder diffractometer D1A is still unique in being able to provide high resolution at long wavelengths, with shorter wavelength contamination eliminated by the guide tube. D1A is particularly suited to magnetic structures and other large d-spacing studies, such as zeolites.

Back to ILL Homepage
www > Instruments & Support > Instruments & groups > D1A > Characteristics

Instrument Description

Guide hall n°1, thermal guide H22


Monochromator

30 Ge crystals, 30 mm high

take-off angle

122°

Ge [hkl]

wavelengths λ/Å

117

1.390

335

1.514

115

1.911 (optimum λ)

113

2.994
(0.1 % λ /3 contamination)

beam size at sample

20 x 30 mm< SUP > 2 < SUP >

flux at sample

2 x 106 n cm-2s-1

Resolution

2θ

FWHM

30°

0.50°

60°

0.41°

90°

0.32°

120°

0.33°

150°

0.97°

angular ranges

6° < 2θ < 160°


0° < ω < 360°

Detectors

25 3He counters at 5 atm

efficiency

90 % at 1.5 Å

collimator

transmission 96 %

background without sample

0.04 Hz

Sample environment

cryostat temperature

1.5 ... 300 K

cryofurnace temperature

1.5 ... 600 K

furnace temperature

< 1000 °C

D1A is a reliable instrument for standard crystallographic problems. It gives excellent results with the Rietveld method owing to its near perfect Gaussian peak-shape in the 2θ-range 30° to 150°.

Complete scans take 2 to 10 hours. Crystal structures with low-symmetry unit cells and with cell volumes up to about 1000 Å3 may be satisfactorily refined. The high resolution over a wide range of scattering angles permits the refinement of up to 150 structural parameters by the Rietveld method.


Special features include

  • a high take-off angle of 122°, giving high resolution at large scattering angles (up to 160°);
  • a bank of 25 high efficiency collimators and counters;
  • an anisotropically squashed germanium monochromator focussing a 250 mm high beam onto only 30 mm;
  • a wide choice of wavelengths, from 1.39 Å to 2.99 Å, quickly available by simple rotation of the focussing monochromator;
  • programmed temperature control for cryo-stats and furnaces.

 

The large monochromator take-off angle means that the diffraction pattern is focussed for the parallel geometry shown (2θ = 122°). The counter can be swept through 0° to 2θ = 160° for the highest angle counter, usually in steps of 0.05°.

To top