Recently there have been many studies of different com-rally with two stable isotopes, 69 Ga and 71 Ga. Both isotopes have nuclear spin 3 2 . We chose 71 Ga isotope for our studies. posite materials with characteristic sizes of the order of several nanometers, including filled porous media. Nanostruc-Measurements were performed within the temperature tures are the object of great interest because of various potenrange 140 to 370 K. While the melting point of bulk gallium tial applications. Due to the possibility of investigation of is 302.8 K, the restricted gallium can remain liquid well size effects, surface phenomena, and influence of confined below this point (5). The temperature was changed to the geometry, nanostructures are also very attractive from a funtarget value at a rate of 0.5 K/min. After temperature stabilidamental point of view (1-6).
zation, the sample was kept for about five minutes prior to Here we present the first NMR studies of liquid gallium spectral acquisition. confined within a porous opal-like medium which is a regular A nuclear resonance for liquid 71 Ga in the opal at 310 K packed array of silica spheres of 2500 A Λin diameter. This is shown in Fig. 1a. It consists of two components: a broad medium has been described in detail elsewhere (7) and we high-field component and an additional narrow low-field will refer to it below as opal. Voids between the spheres, component, marked by the arrow in Fig. 1a. Within the which can be treated as a kind of pore, take up approximately temperature range considered, there were no noticeable 25% of the sample volume and form a regular three-dimenchanges in widths of these line components; hence the broadsional thorough interconnected network. Gallium was inening of the NMR line should not be dominated by the serted into the opal under high pressure up to 9 kbar and voids were filled to about 85%. Thus there is a three-dimensional gallium network within connected pores. Gallium is a remarkable metal, noted for its specific properties in comparison with other elements of its group (8-14). The purpose of the present investigation is to combine these attractive features with the added features of a nanostructured medium.
Experiments were performed on a Bruker MSL300 spectrometer in a constant magnetic field of B 0 Γ 7 Tesla, which corresponds to a 71 Ga nuclear Larmor frequency, n 0 , of 91.6 MHz. The spectral width was 10 6 Hz. A dead-time delay equal to 5 ms and a recycle delay equal to 10 ms were used. Spectra were sampled in 2K data points and were obtained accumulating 30,000 free induction decays. The sample was mounted in a Doty DSI418 probehead. The FID was acquired after a single pulse. The amplitude of the RF field was 4.5 G. Experiments were also carried out on bulk Ga as a reference material. Gallium is a Group III element which occurs natu-* To whom correspondence should be addressed.