Volume 98, Number 6, June 2012
|Number of page(s)||6|
|Section||Condensed Matter: Structural, Mechanical and Thermal Properties|
|Published online||10 July 2012|
An unexpected softening from WB3 to WB4
1 College of Engineering Science and Technology, Shanghai Ocean University - Shanghai 201306, China
2 State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences - Shanghai 200050, China
3 School of Aerospace Engineering and Applied Mechanics, Tongji University - Shanghai 200092, China
Received: 22 March 2012
Accepted: 4 June 2012
We report a drastic reduction of hardness of about 61% from WB3 to WB4. The three-dimensional covalent network consisting of boron honeycomb planes interconnected with strong zigzag W-B bonds underlies the high hardness of WB3. Despite the strong intralayer and interstitial B-B bonds, the interlayer B-B nonbonding and the considerably weak zigzag W-B bonding allow the layers of WB4 to cleave readily, which results in the anomalous softening of WB4. The results provide robust evidence that the highest boride of tungsten, which is characterized experimentally by an inexpensive superhard material, should be stoichiometric WB3, not WB4.
PACS: 62.20.-x – Mechanical properties of solids / 71.20.Be – Transition metals and alloys / 81.05.Zx – New materials: theory, design, and fabrication
© EPLA, 2012
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