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A combination of X-ray techniques [diffraction and Zr K-edge absorption (EXAFS and XANES)] and multinuclear (1H, 13C, 17O) solid-state NMR spectroscopy is employed to follow in detail the structural development of nanocrystalline zirconia. 17O magic-angle spinning NMR spectroscopy of sol−gel produced undoped ZrO2 shows unequivocally that oxygen sites in the initial gel are monoclinic-like. This result is consistent with X-ray absorption measurements, which also suggest that the structures of the initial amorphous phases of doped and undoped samples produced by the hydroxide-precipitation and sol−gel methods are very similar. On crystallization, the local structure of the crystalline component is tetragonal, but a significant fraction of the sample remains disordered. Heating to higher temperatures results in conversion to monoclinic zirconia in undoped samples at room temperature. For sol−gel-produced ZrO2, 13C NMR shows that loss of all of the organic fragments occurs prior to crystallization. The 1H NMR experiments determined that the proton content remains significant until well above the crystallization temperature, so that the composition is not accurately described as ZrO2 until >500 °C.

Nuclear quadrupole resonance is a radio frequency (rf) spectroscopic technique, closely related to NMR, which can be used to detect signals from solids containing nuclei with spin quantum number >1/2. It is nondestructive, highly specific and noninvasive, requires no static magnetic field, and as such is currently used in the detection of explosives and narcotics. Recent technological advances in pulsed NQR methods have shortened detection times, eliminated spurious signals, and enhanced the sensitivity of detection of 14N frequencies, which lie in the low rf range of 0.4-6 MHz, encouraging a wider range of "real world" applications. This Perspective highlights some of the advantages of NQR, the applications in which it could be used, such as the quantification of pharmaceuticals and the identification of polymorphs. Other roles could include detection, analysis, and quality control of pharmaceuticals at all stages of manufacture. Finally, recent advances which enhance even further the sensitivity of detection will be discussed.