29 Jun 2015

Copper Oxide Crystal Growth

Literature Discussion

Submitted by Ellen Steinmiller, University of Dallas
Categories
Description: 

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.  

Learning Goals: 

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 

Implementation Notes: 

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. 

Time Required: 
50 minutes
Evaluation
Evaluation Methods: 

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. 

Evaluation Results: 

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.

Creative Commons License: 
Creative Commons Licence

Comments

HI all,

A good companion LO for this one is George Lisensky's solid state stoichiometry online available here  https://www.ionicviper.org/web-resources-and-apps/solid-state-stoichiometry-online

In the "advanced unit cells" site provided in George's LO, Cu2O is one of the unit cell options.  I used this today when I discussed an earlier Choi / Siegfried Cu2O article with my nanomaterials class. I projected the unit cell and showed how the (100) plane has only oxide ions while the (110) has Cu ions directly on it.

Also of note and related to this literature discussion is a more recent JACS article on solution-phase Cu2O oxide particle synthesis (with control of shape) and resulting differences in catalytic efficiency. The article is JACS 2012, 134, 1261-1267.  There's also a nice Nature "news and views" summary / analysis of the 2012 article by Peidong Yang at Nature 2012, 482, 41-42.

This is all very fun stuff, and I think students enjoy the visual aspect of the cubes, octahedra, and everything in between.

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