RESUMO
The thermal transformation of the tetragonal-zircon (tz-) to tetragonal-scheelite (ts-)BiVO4 was studied by inâ situ synchrotron X-ray diffraction, thermogravimetric analysis, and Fourier-transformed infrared spectroscopy. Upon heating, the tetragonal zircon polymorph of BiVO4 (tz-BiVO4) transitioned to the ts-polymorph between 693-773â K. Above 773â K, single phase ts-BiVO4 was observed before transitioning to the monoclinic fergusonite (mf-) polymorph upon cooling. An anomaly in thermal expansion was observed between 400-500â K, associated with the loss of intercalated H2O/NH4 + from the coprecipitation procedure. Heating tz-BiVO4 resulted in contraction of the V-O bond distance and VO4 polyhedra volume, ascribed to rotation of the tetrahedra groups. Attempts to study this by neutron diffraction failed due to the large incoherent scatter from the hydrogenous species. Efforts to remove these species while maintaining the tz-BiVO4 structure were unsuccessful, suggesting they play a role in stabilizing the tz-polymorph. The local structure of both mf-BiVO4 and tz-BiVO4 were investigated by X-ray pair distribution function analysis, revealing local distortions.
RESUMO
This study in 2005 compared the need for mental health services, actual use of services and barriers to use by 3 groups in Shiraz city in the Islamic Republic of Iran: a sample of the general population, parents of children with mental illness and primary-school teachers. Among the general population, 76.0% reported that they had wanted help in the previous 6 months and, of these, 50.0% actually sought it. The rates for parents of children with mental problems were 81.3% and 55.4% and for teachers were 60.0% and 35.0% respectively. The most common barriers to service use were logistic, especially the cost of and inconvenient access to services. Barriers related to perceptions of mental health services were also important, such as lack of trust and perceptions of friends/family