Solid State Nuclear Magnetic Resonance 26 (2004) 114–120 Application of fast amplitude-modulated pulse trains for signal enhancement in static and magic-angle-spinning 47;49 Ti-NMR spectra Thomas Bra¨uniger, a, * P.K. Madhu, b Andre´ Pampel, c and Detlef Reichert a a Department of Physics NMR Group, University of Halle, Friedemann-Bach-Platz 6, 06108 Halle, Germany b Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India c Universita¨t Leipzig, Fakulta¨t fu¨r Physik und Geowissenschaften, Linne´strasse 5, 04103 Leipzig, Germany Received February 2, 2004; revised February 19, 2004 Abstract It is demonstrated that the use of fast amplitude-modulated RF pulse trains with constant (FAM-I) and incremented pulse durations (SW–FAM) leads to considerable sensitivity enhancement for the central-transition signal (via spin population transfer from the satellite transitions) for solid-state NMR spectra of titanium, 47 Ti ðI ¼ 5 2 Þ and 49 Ti ðI ¼ 7 2 Þ: For the magic-angle spinning spectra of TiO 2 and BaTiO 3 ; the intensity of the 49 Ti central-transition line was more than doubled compared to simple Hahn-echo acquisition, while for the static case, enhancement factors of 1.6 ðTiO 2 Þ and 1.8 ðBaTiO 3 Þ were obtained. No lineshape distortions are observed in either MAS or static spectra of both compounds. Employment of the FAM and SW–FAM sequences should be useful in the routine acquisition of 47;49 Ti spectra, as the NMR signal can be detected much faster. r 2004 Elsevier Inc. All rights reserved. Keywords: 47;49 Ti-NMR spectroscopy; TiO 2 , BaTiO 3 ; Signal enhancement; SW–FAM pulses 1. Introduction Nuclear magnetic resonance (NMR) spectroscopy has become a useful technique for characterisation of solid inorganic materials such as minerals, ceramics, catalysts and glasses [1], primarily because of its capability to selectively probe the local environment of atomic nuclei. The large majority of NMR-observable nuclei in inorganic materials have half-integer spins I 4 1 2 ; and thus possess a quadrupolar moment [2]. A quadrupolar nucleus of special technological and scientifical interest is titanium, as it occurs in ferroelectric, piezoelectric and pyroelectric materials [1]. Accordingly, solid-state tita- nium NMR has been employed for examining technolo- gically important compounds such as titania, TiO 2 [3–5], barium titanate, BaTiO 3 [3,4,6–8], metal alloys [4] and zeolites [9]. Investigations of a range of ATiO 3 and A 2 TiO 4 compounds by Dupree and co-workers [10,11] have showed that a correlation between NMR interaction parameters of titanium nuclei and local structure exists. However, compared to some other quadrupolar nuclei with half-integer spin, the number of published titanium NMR studies is relatively small. This is chiefly due to the properties of the two magnetically active isotopes, 47 Ti and 49 Ti; which make observing these nuclei intrinsically difficult. As can be seen from Table 1, low natural abundance and low-resonance frequencies result in very low detection sensitivity for both isotopes. (Since the resonance frequencies for 47 Ti and 49 Ti are only E11kHz apart even at a magnetic field strength of 17:6T; both isotopes will appear in the same spectrum, sometimes with overlapping lines.) The small gyromag- netic ratios ðgÞ of 47 Ti and 49 Ti also mean that their resonance frequencies will be below the observable range for most NMR spectrometers with moderate magnetic field strength. In addition, because of fairly large quadrupole moments Q (see Table 1), the central-transition lines of titanium are rather broad. Compared to the often observed 27 Al nucleus, the relative second-order quadrupolar broadening factor, ðQ 2 =gÞ½ðI ðI þ 1Þ 3 4 Þ=ð2I ð2I  1ÞÞ 2 ; of 49 Ti lines is greater by about 5.7 for sites with the same structural distortion [13]. The 47 Ti resonances are broadened even ARTICLE IN PRESS *Corresponding author. Fax: +49-345-5527161. E-mail address: braeuniger@physik.uni-halle.de (T. Bra¨uniger). 0926-2040/$-see front matter r 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ssnmr.2004.02.003