Studies on the properties of zinc oxide (ZnO) have been well-reviewed, 1À3 with many applications proposed such as thin-film solar cells 1 and optoelectronic materials. 3 The performance of doped ZnO as a transparent conducting oxide (TCO) prepared using techniques such as magnetron sputtering, chemical vapor deposition, and pulsed laser deposition has provided a solid body of knowledge. 1 Zn is cheap and abundant, making doped ZnO a favored candidate to replace TCOs based on indium tin oxide (ITO) for thin-film photovoltaic applications. Typical dopants used to prepare ZnO-based TCOs include F, B, Al, Ga, In, and Sn. The solÀgel route has been proposed as a cost-effective alternative to vacuumassisted deposition of films for large-area TCOs, and a number of studies have examined the influence of processing details (heating profile, temperature, solvents, etc.) on film properties and performance. 4À20 However, despite the identification of optimum processing conditions, there is limited understanding as to how and why the processing variables influence electrical properties such as resistivity. Previous studies have shown, for example, that the texturing and resistivity of solutionprocessed films are sensitive to both the concentration 5 and heating profiles used to calcine the films. 6,7 Rapid thermal annealing appears to result in highly (002)-oriented films with low resistivities, 7,8 agreeing with other observations that higher conductivities and transmittances occur in preferred (002)-oriented films. 10 However, other studies appear to suggest that more random orientations are preferred. 11 There is general agreement that ZnO:Al TCOs with low resistivities appear to require around 1 at. % added Al dopant and postsynthesis annealing at ca. 400À500°C. 8À14 Estimates of lattice deformation made from X-ray diffraction (XRD) data using Bragg's equation to attempt to quantify the effective dopant concentration suggest that the effective Al concentration is much lower than the added Al concentration. 12 A dopant ion introduced to modify the electronic properties of a material needs to be incorporated into the crystal structure of the host material (either in lattice sites or interstitially). In the case of a ZnO:Al TCO, the Al 3+ ion is required to occupy a Zn 2+ lattice site in order to provide a free electron (charge carrier) and enhance the conductivity of the ZnO. A simplistic representation is shown, 1, in which an Al 3+ ion occupies the site of a Zn 2+ ion, producing a charged defect. 14 A quantum chemical approach has been applied to calculate the structural, electrical, and electronic properties of ZnO due to the Al doping and explains the increase in the n-type electrical conductivity. 15 To ABSTRACT: We report the discrimination of Al doping sites in solÀgel-formed ZnO powders by solid-state 27 Al nuclear magnetic resonance (NMR) spectrometry. A degree of control of dopant placement is demonstrated by modifying sol precursors and processing parameters. ZnO powders containing 1À8 at. % aluminum ions were ...

The grain growth kinetics of Al-doped ZnO nanocrystalline powders have been studied using in situ, real-time synchrotron X-ray diffraction measurements during calcination at various temperatures (400–800 °C) from sol–gels with varying levels of Al dopant (0–4 mol %). Development of the crystallite size versus time was described using a relaxation model. A grain growth activation energy of 24 ± 3 kJ/mol was obtained for undoped ZnO, while for all of the Al-doped ZnO experiments the activation energy was 43 ± 4 kJ/mol. This difference is attributed to the segregation of Al to the crystallite interfaces, where it interferes with the ZnO grain growth, by inhibiting the motion of atoms across the grain boundaries.

Using different organomercury substrates, two isomeric cycloaurated complexes derived from the stabilised iminophosphorane Ph 3 P=NC(O)Ph were prepared. Reaction of Ph 3 P=NC(O)Ph with PhCH 2 Mn(CO) 5 gave the manganated precursor (CO) 4 Mn(2-C 6 H 4 C(O)N=PPh 3), metallated on the C(O)Ph substituent, which yielded the organomercury complex ClHg(2-C 6 H 4 C(O)N=PPh 3) by reaction with HgCl 2 in methanol. Transmetallation of the mercurated derivative with Me 4 N[AuCl 4 ] gave the cycloaurated iminophosphorane AuCl 2 (2-C 6 H 4 C(O)N=PPh 3) with an exo PPh 3 substituent. The endo-isomer AuCl 2 (2-C 6 H 4 Ph 2 P=NC(O)Ph) [aurated on a PPh 3 ring] was obtained by an independent reaction sequence, involving reaction of the diarylmercury precursor Hg(2-C 6 H 4 P(=NC(O)Ph)Ph 2) 2 1 [prepared from the known compound Hg(2-C 6 H 4 PPh 2) 2 and PhC(O)N 3 ] with Me 4 N[AuCl 4 ]. Both of the isomeric iminophosphorane derivatives were structurally characterised, together with the precursors (2-HgClC 6 H 4)C(O)N=PPh 3 and (CO) 4 Mn(2-C 6 H 4 C(O)N=PPh 3). The utility of 31 P NMR spectroscopy in monitoring reaction chemistry in this system is described.

a b s t r a c tReaction of the metalloligand [Pt 2 (l-S) 2 (PPh 3 ) 4 ] with 0.5 mol equivalents of durene-1,4-bis(mercuric acetate) [AcOHgC 6 Me 4 HgOAc] in methanol gives the polynuclear complex [{Pt 2 (l-S) 2 (PPh 3 ) 4 } 2 (l-1,4-C 6 Me 4 Hg 2 )] 2+ , isolated as its PF À 6 and BPh À 4 salts. Positive-ion ESI mass spectra indicate that [{Pt 2 (l-S) 2 (PPh 3 ) 4 } 2 (l-1,4-C 6 Me 4 Hg 2 )] 2+ undergoes fragmentation by successive loss of PPh 3 ligands, while the ESI mass spectrum of the BPh À 4 salt showed additional ions [Pt 2 (l-S) 2 (PPh 3 ) 4 (HgC 6 Me 4 HgPh)] + and [Pt 2 (l-S) 2 (PPh 3 ) 4 HgPh] + as a result of phenyl transfer from BPh À 4 to Hg. A single-crystal X-ray structure determination on [{Pt 2 (l-S) 2 (PPh 3 ) 4 } 2 (l-1,4-C 6 Me 4 Hg 2 )](BPh 4 ) 2 shows that the cation crystallises on a centre of symmetry, with structural features that are comparable to those of the previously characterised complex [Pt 2 (l-S) 2 (PPh 3 ) 4 HgPh]BPh 4 .