Students in a 2nd year inorganic class read an article describing the effect of additives on the final morphology of copper oxide. (Siegfried, M.J., and Choi, K-S, “Elucidating the Effect of Additives on the Growth and Stability of Cu2O Surfaces via Shape Transformation of Pre-Grown Crystals”J. Am. Chem. Soc., 2006, 128 (32), pp 10356–10357. dx.doi.org/10.1021/ja063574y). The authors describe a systematic method that exploits the preferential adsorption phenomenon to regulate crystals shapes by observing the shape transformation of pre-grown crystals over time (e.g cubic to rhobooctahedral to octahdral and back). The authors start with seed crystals of specific morphology and then immerse the pre-grown crystals in a second solutions with additives to direct the crystal growth. This strategy allowed them to develop a general scheme to determine the relative order of surface energies and form new crystal shapes containing planes that cannot be directly stabilized by preferential adsorption alone.
After reading and discussing this paper, students will be able to:
- Differentiate between notations describing planes, directions, and families of planes
- Describe atomic surface terminations of different crystal faces of the same unit cell
- Describe the effect of common additives on synthesis of crystals
- Determine d-spacings of planes from XRD data
- Determine lattice parameters from XRD data
I used this article in the Spring of 2014 in a class of 9 (1 freshmen, 1 sophomore, 5 juniors, 2 seniors) as our conclusion of our discussion of solid state chemistry. Students had a background in electrochemistry, crystal structures and x-ray diffraction before reading this paper. Students were required to submit the first set of questions when they came to class and then they worked on the second set of questions in small groups. During the class discussion, we reviewed electrochemistry, in particular the reaction of electrodeposition of Cu2+ to Cu2O and revisited Pourbaix diagrams briefly to discuss stability of different metal oxide species. We also discussed preferential adsorption and how this impacts crystal growth. For a good paper on preferential absorption, see Matthew J. Siegfried and Kyoung-Shin Choi, “Electrochemical Crystallization of Cuprous Oxide with Systematic Shape Evolution,” Adv. Mater. 2004, 16, 1743-1746. (dx.doi.org/ 10.1002/adma.200400177). Schematic 1 is particularly helpful and I used it to develop the concept preferential adsorption and the relative enrgies of planes.
Student answers to the reading comprehension questions were collected at the beginning of class and graded out of 10 points. An additional 15 points was based on on class participation during the discussion and answers to the in class questions.
Overall, students did well on this paper. During the group problems, students struggled the most with Miller indexes and drawing the layer diagrams of the Cu atoms. In the future I would incorporate ICE models in the class discussion so that students can more clearly see the different crystal planes. Students are often quite confused as to why copper oxide is a primitive cubic cell and I think see the models would help with the visualization that not all Cu atoms are created equally.