ABSTRACT
The Raman spectra of seven A(2)MWO(6) tungstate double perovskites are analysed. Ba(2)MgWO(6) is a cubic double perovskite with Fm3[combining macron]m symmetry and its Raman spectrum contain three modes that can be assigned in a straightforward manner. A fourth mode, the asymmetric stretch of the [WO(6)](6-) octahedron, is too weak to be observed. The symmetry of Ba(2)CaWO(6) is lowered to tetragonal I4/m due to octahedral tilting, but the distortion is sufficiently subtle that the extra bands predicted to appear in the Raman spectrum are not observed. The remaining five compounds have additional octahedral tilts that lower the symmetry to monoclinic P2(1)/n. The further reduction of symmetry leads to the appearance of additional lattice modes involving translations of the A-site cations and librations of the octahedra. Comparing the Raman spectra of fourteen different A(2)MWO(6) tungstate double perovskites shows that the frequency of the symmetric stretch (ν(1)) of the [WO(6)](6-) octahedron is relatively low for cubic perovskites with tolerance factors greater than one due to underbonding of the tungsten and/or M cation. The frequency of this mode increases rapidly as the tolerance factor drops below one, before decreasing gradually as the octahedral tilting gets larger. The frequency of the oxygen bending mode (ν(5)) is shown to be dependent on the mass of the A-site cation due to coupling of the internal bending mode with external A-site cation translation modes.
ABSTRACT
Family values regarding appropriate attitudes and behaviors are communicated to children from birth. Society's values begin to affect the child at an early age and as these change, so do children's beliefs and attitudes. A change in society's values toward smoking has been evidenced in the last decade by increased social sanctions against smoking and increased militancy of nonsmokers. This longitudinal Primary Grades Health Curriculum Project investigates the relationship between an activity-centered experiential health education program and: 1) positive health attitudes; 2) experimentation use and future expectancy to engage in cigarette smoking; and 3) changes in smoking behavior among the children's parents. Six hundred students in two New York school districts were pretested in their kindergarten year in 1977 on entry level of knowledge and attitudes about health. The results reported here from data collected at the end of third grade indicate that the experimental group possessed more positive attitudes about health, showed less exposure to experimentation with alcohol among their friends and less engagement in smoking cigarettes. A significant number of parents of experimental group students reported that they had changed their smoking habits since their child had entered school as a result of their children's health program.
