Crystallization of amorphous aluminium phosphate investigated by synchrotron X-ray diffraction

216

Nuclear Instruments and Methods in Physics Research A261 (1987) 216 218 North-Holland, Amsterdam

CRYSTALLIZATION OF AMORPHOUS ALUMIN1UM BY S Y N C H R O T R O N X - R A Y D I F F R A C T I O N F. N E I S S E N D O R F E R

PHOSPHATE

INVESTIGATED

a n d U. S T E I N I K E

Central Institute of Physical Chemistry, Academy of Sciences of GDR, DDR-1199 Berlin, Germany B.P. T O L O C H K O Institute of Solid State Chemistry, Sibirian Branch of Academy Sciences of USSR, Novosibirsk-91, USSR M.A. SHEROMOV Institute of Nuclear Physics, Sibirian Branch of Academy Sciences of USSR, Novosibirsk-90, USSR

The crystallization of amorphous aluminium phosphate was investigated by X-ray diffraction of synchrotron radiation with a time resolution 1 s. Information about the evolution of long-range order (crystal structure) and the short-range order (differential radial distribution function) during crystallization was obtained.

1. Introduction For the investigation of very fast processes by diffraction methods it is necessary to use a synchrotron radiation source. In our investigations we observed the crystallization of amorphous aluminium phosphate and it was possible to register in situ the changes of the order structure by X-ray synchrotron radiation (SXRD). The investigations were performed with synchrotron radiation from the storage ring VEPP-4.

2. Experimental The sample used in this investigation was precipitated amorphous aluminium phosphate, A1PO4 (VEB Laborchemie Apolda). The powder sample was placed

Fig. 1. The principle of the developed heater. 0168-9002/87/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

on a heater (fig. 1), which was developed as an attachment to the Philips-X-ray goniometer PW 1050. Up to 350 o C (voltage = 245 V) a linear heating curve is possible with this heater. The temperature of the sample was measured by a chromel alumel thermocouple. 10 crystallization curves with 20 diffraction pictures (KADR), respectively, were accumulated. The investigations were performed with synchrotron radiation from storage ring VEPP-4 (5154 MeV; 6.6 mA). The synchrotron radiation was monochromated by a Ge(111)-crystal, so that the wavelength used was 0.0524 nm. The diffracted intensity was registered with a one-coordinate-detector [1]. Fig. 2 shows the schematic details of the experimental arrangement.

3. Results and discussion The registration of the SXRD-diagrams was carried out by the computer-program K I N O [2]. The aim of the experiments was to investigate the changes in the order structure during the crystallization processes: (1) The development of long-range order (crystal structure) is clearly demonstrated in the diffraction pictures. Fig. 3 shows a traditional X-ray diffraction diagram of an A L P O 4 sample, tempered at 300 o C for 3 h. A crystobalit modification is formed. In this modification aluminium phosphate has a tetrahedral structure comparable with quartz [3]. (2) The short-range order can be determined by the method of differential radial distribution function ( D R D F ) [4]. In this case the experimental intensity was

F Neissendorfer et al. / S X R D study of crystallization o f A l P O 4

217

VEPP4

Fig. 2. S c h e m a t i c details of the e x p e r i m e n t a l a r r a n g e m e n t s : 1 one c o o r d i n a t e - d e t e c t o r ; 2 - G e ( l l l ) - m o n o c h r o m a t o r ; 3 digital counter; 4 - v o l t - m e t e r ; 5 - m o t o r control, 6 - h e a t e r (245 V ) .

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Fig. 4. D R D F - c u r v e s of A I P O 4 D o t t e d curve: TRF_£1, K A D R 1; solid curve; TRFAI, K A D R 20. V. X - R A Y D I F F R A C T O M E T R Y

218

F. Neissendorfer et aL / SXRD study of crystallization of AlPO 4

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(3) The first peak (at 0.16 nm) a n d the second one of the D R D F - c u r v e s were determined for tetrahedral P O 4 and A104. There are n o significant differences a n d this means that the tetrahedral structure is the same in the a m o r p h o u s state a n d in the crystalline state after crystallization at 300 ° C. In fig. 5 the sum of pair distribution functions ( P D F ) [6] are shown, calculated with the F O R T R A N subroutine P A I R a n d the atomic distances of berlinite given by ref. [7]: P-O 0.1516 n m A1-O 0.1736 n m O-O 0.2475 n m (PO4-tetrahedra) O-O 0.2840 n m (AIO4-tetrahedra) A1 P 0.3080 nm.

Rlnm Fig. 5. Comparison of calculated PDF with atomic distances of berlinite [7].

References

scaled to absolute electron units. After this procedure the D R D F - c u r v e was o b t a i n e d by Fourier transformation of the corrected a n d scaled intensities [5]. The estimated D R D F - c u r v e s of a m o r p h o u s A L P O 4 (TRE~, K A D R 1) a n d of the crystallized A L P O 4 (TRE0, K A D R 20) are d e m o n s t r a t e d in fig. 4.

[1] [2] [3] [4] [5] [6] [7]

S.E. Baru et al., Nucl. Instr. and Meth. 152 (1978) 195. A.A. Basina et al., INP-Report (Novosibirsk 1981) 20. O.W. Fl5rke, Z.f.Kristallographie 125 (1967) 134. F. Neissendorfer, Acta Polymerica 33 (1982) 395. S. Steeb, Springer Tracts in Modern Physics 47 (1968) 1. L. Cervinka et al., J. Non-Cryst. Solids 34 (1979) 275. D. Schwarzenbach, Z.f.KristaUographie 123 (1966) 161.