A thermodynamic model based on published data is presented for calculating the solubility and speciation of ZnO in aqueous solutions as a function of pH, ammonia concentration, and temperature. These calculations are used to explain how solubility and speciation control nucleation and growth behavior from an aqueous solution. The nucleation and growth behavior, in turn, can lead to the different morphologies of epitaxial and particulate ZnO obtained experimentally using low temperature aqueous methods. The calculations indicate that the presence of the zinc amine complex, Zn(NH 3 ) 4 2+ , causes ZnO to display a substantial decrease in solubility when the temperature is raised from room temperature to 90 °C. This retrograde solubility is the basis for a novel continuous circulation reactor for synthesizing ZnO, which is presented in part 2 of this series.

No abstract

Using either an ammoniacal route, the reaction between DyCl3, Na0, and HOR in liquid ammonia, or preferentially reacting Dy(N(SiMe3)2)3 with HOR in a solvent, we isolated a family of dysprosium alkoxides as [Dy(mu-ONep)2(ONep)]4 (1), (ONep)2Dy[(mu3-ONep)(mu-ONep)Dy(ONep)(THF)]2(mu-ONep) (2), (ONep)2Dy[(mu3-ONep)(mu-ONep)Dy(ONep)(py)]2(mu-ONep) (3), [Dy3(mu3-OBut)2(mu-OBut3(OBut)4(HOBut)2] (4), [Dy3(mu3-OBut)2(mu-OBut)3(OBut)4(THF)2] (5), [Dy3(mu3-OBut)2(mu-OBut)3(OBut)4(py)2] (6), (DMP)Dy(mu-DMP)4[Dy(DMP)2(NH3)]2 (7), [Dy(eta6-DMP)(DMP)2]2 (8), Dy(DMP)3(THF)3 (9), Dy(DMP)3(py)3 (10), Dy(DIP)3(NH3)2 (11), [Dy(eta6-DIP)(DIP)2]2 (12), Dy(DIP)3(THF)2 (13), Dy(DIP)3(py)3 (14), Dy(DBP)3(NH3) (15), Dy(DBP)3 (16), Dy(DBP)3(THF) (17), Dy(DBP)3(py)2 (18), [Dy(mu-TPS)(TPS2]2 (19), Dy(TPS)3(THF)3 (20), and Dy(TPS)3(py)3 (21), where ONep = OCH2CMe3, OBut) = OCMe3, DMP = OC6H3(Me)(2)-2,6, DIP = OC6H3(CHMe2)(2)-2,6, DBP = OC6H3(CMe3)(2)-2,6, TPS = OSi(C6H5)3, tol = toluene, THF = tetrahydrofuran, and py = pyridine. We were not able to obtain X-ray quality crystals of compounds 2, 8, and 9. The structures observed and data collected for the Dy compounds are consistent with those reported for its other congeners. A number of these precursors were used as Dy dopants in Pb(Zr0.3Ti0.7)O3 (PZT 30/70) thin films, with compound 12 yielding the highest-quality films. The resulting Pb0.94Dy0.04(Zr0.3Ti0.7)O3 [PDyZT (4/30/70)] had similar properties to PZT (30/70), but showed substantial resistance to polarization reversal fatigue.

The formation of pores has been observed in epitaxial ZnO films deposited from low temperature aqueous solution when annealed at 300 °C and higher. The effects of these pores could have a dramatic impact on the ability to utilize low temperature aqueous synthesis to deposit ZnO films for optoelectronic devices. The results of thermogravimetric analysis, evolved-gas mass-spectrometry, and secondary ion mass spectrometry analysis indicate that the formation of pores is related to the expulsion of water vapor from the ZnO crystal. We propose that the pores form via the coalescence of zinc and oxygen vacancies that result from the incorporation, and subsequent removal, of a large concentration of hydroxide ions substituting for oxygen in the ZnO lattice. Despite the large change in solid volume undergone during pore formation, the ZnO films remain single phase and epitaxial and retain good electrical conductivity.

Flat panel display technology seems to be an ever-expanding fi eld developing into a multibillion dollar market. A set of technical solutions involve a transparent conducting fi lm (TCF) that is today still dominated by indiumtinoxide (ITO). In a race to fi nd alternatives that would avoid the indium pitfalls, mainly due to its increasing price and limited natural availablity, replacement materials have been extensively investigated. This work demonstrates that by exploiting basic principles of crystal growth in geometrically constrained conditions, zinc oxide (ZnO) could easily be utilized for this purpose. ZnO layers were grown on inexpensive glass substrates via lowtemperature citrateassisted hydrothermal (HT) method. It was shown that in the nucleation stage the crystal growth can be effi ciently controlled by spatially confi ned oriented growth (SCOG) mechanism to produce smooth and dense (0001) oriented polycrystalline ZnO fi lms with superb optical properties. Our products show optical transparency of 82% and surprisingly low sheet resistance for undoped ZnO, only in the order of few 100 Ω sq − 1 . We believe that a very high degree of selforganization between the ZnO crystals in our polycrystalline fi lms grown under controlled SCOG conditions is main reason for the highest so far reported transparency to conductivity ratio for undoped ZnO thin fi lm ceramics.conductivity which meet the high standards for many photonic and/or electronic applications.