Single hydrothermal method

The hydrothermal method for producing single crystals of quartz works by taking advantage of the slight solubility of SiOa) ) in supercritical water ... 

Key words Point defects, photoluminescence, photo-EPR, single crystals, hydrothermal method, exciton, donor, acceptor, thermoluminescence... 

In the present work, we investigated powders, films and single crystals of ZnO produced by the hydrothermal method at the Institute of Crystallography of the Russian Academy of Sciences and by the method of gas-transport reactions at the Institute for the Physics of Semiconductor of the Siberian Branch of the Russian Academy of Science. ... 

Hydrothermal/solvethermal s)mthesis of RMO3 is also extensively adopted, by virtue of the low reaction temperature and well-crystallized products. Vazquez-Vazquez and Lopez-Quintela (2006) reported the solvothermal synthesis of Lai j-A MnOs (A = Ca, Sr, Ba) NPs in benzyl alcohol and acetophenone. The obtained precipitate was annealed to form crystalline products and acetophenone was found to be more suited to obtain clean perovskite phase. Zhu et al. (2008a) prepared single-crystalline YbMnOs and LuMnOa nanoplates via hydrothermal method. The products were found to be hexagonal phases. A possible formation mechanism was proposed, which involves the formation of ROOH phase as intermediate. 

These mixed oxides have been considered as nonlinear optical materials (see Nonlinear Optical Materials). They crystallize as ordered derivatives of the cristobalite structure. As early X-ray structural studies were performed on twinned crystals grown from congment melts, their true symmetry was not firmly established. Untwinned single crystals have been produced by hydrothermal methods, and the space group has been convincingly established as 14. 

Single crystals of rare earth hydroxides can be obtained by a hydrothermal method. At 190 20 °C and from 1.2 x 10 to 7 x 10 Pa, rare earth hydroxides can be grown from RE203-H20-Na0H systems after prolonged treatment. 

The hydrothermal method has been used to prepare monodispersed ZnS (6 nm) [10] and CdS nanocrystals (16 nm) [11]. By hydrothermal polymerization and simultaneous sulfidation processes, nanocomposites CdS/poly(vinyl acetate) nanorods [12] and nanospheres [13] were synthesized. In aqueous hydrazine solutions, nonstoichiometric metal telluride nanocrystallites such as Cu2.86Te2, CuyTes, Cuy-xTe, and Ag7Te4 [14], and cubic CogSg were hydrothermally synthesized [15]. Other transition metal chalcogenides, such as single-molecular-layer M0S2 [16] and MoSey [17] were also prepared under hydrothermal conditions. 

Hydrothermal methods can be used to form solid state materials, providing the reactants are soluble. Slow cooling from solution can be one way to form single crystals. 

The principles discussed in Topic E4 can often be used to choose an appropriate counter-ion (for example one of similar size) to achieve the desired precipitation. Solubility may also be manipulated by changing the solvent or the temperature. Hydrothermal methods use water under conditions of high temperature and pressure to increase the solubility of reactants. Temperatures between 150 and 500°C may be used, with pressures between 100 and 2000 bar. Hydrothermal methods are common for the synthesis of some solids such as zeolites (see Topic D5) and also for growing single crystals of compounds such as quartz, Si02. 

Single erystal growth by hydrothermal methods utilizes water as the material-transport medium. The method is most often used for growing single crystal quartz. Quartz (Si02) is not very soluble in water, but its... 

Single crystals of praseodymium dioxide and intermediate terbium oxides were grown by the hydrothermal method [126]. The pressure in the sample autoclave was smoothly raised and lowered by control of heating and cooling of the autoclave. The rare earth oxide and nitric acid sealed in capsules of thin-walled gold tubing. The pressure of the capsules was raised to 165 MPa and isobarically heated to the run temperature (1003 1143 K). Holding at least for two hours to reach equilibrium,... 

Pedroni, M., PiccineUi, F., Passuello, T., Gioarola, M., Mariotto, G., Polizzi, S., et al., 2011. Lanthanide doped upconverting colloidal CaF2 nanoparticles prepared by a single-step hydrothermal method toward efficient materials with near infrared-to-near infrared upconversion emission. Nanoscale 3, 1456—1460. 

Lv, B., Liu, Z., Tian, H., Xu, Y, Wu, D., and Sun, Y. Single-Crystalline Dodecahedral and Octodecahedrala-FejOj Particles Synthesized by a Fluoride Anion-Assisted Hydrothermal Method. Advanced Functional Materials, 20(22), 3987-3996 (2010). 

---