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In nanocrystals with thick shells , we furthermore observe a wurtzite to NiAs transformation , which does not occur in the pure bulk materials .
 Chemical: wurtzite; Chemical: NiAs
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: wurtzite; Chemical: NiAs