Spontaneous polarization and piezoelectricity in boron nitride nanotubes

By S. Nakhmanson, A. Calzolari, Vincent Meunier, J. Bernholc, Marco Buongiorno Nardelli. 2003

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Ab initio calculations of the spontaneous polarization and piezoelectric properties of boron nitride nanotubes show that they are excellent piezoelectric systems with response values larger than those of piezoelectric polymers. The intrinsic chiral symmetry of the nanotubes induces an exact cancellation of the total spontaneous polarization in ideal, isolated nanotubes of arbitrary indices. Breaking of this symmetry by intertube interaction or elastic deformations induces spontaneous polarization comparable to those of wurtzite semiconductors. order of magnitude weaker than those of PZT. 3 In this paper, we examine spontaneous polarization and piezoelectricity in boron nitride nanotubes ~BNNT's! in order to estimate their potential usefulness in various pyroelectric and piezoelectric device applications, and to understand the interplay between symmetry and polarization in nanotubular systems. BNNT's, broadly investigated since their initial predic- tion 4 and succeeding discovery, 5 are already well known for their excellent mechanical properties. 6 However, unlike car- bon nanotubes ~CNT's !, most of BN structures are noncen- trosymmetric and polar, which might suggest the existence of nonzero spontaneous polarization fields. Recently, these properties have been partially explored by Mele and Kral, using a model electronic Hamiltonian. 7 They predicted that BNNT's are piezoelectric and pyroelectric, with the direction of the spontaneous electric field that changes with the index of the tubes. The ab initio calculations presented in this pa- per provide a much fuller description and show that BNNT systems are indeed excellent lightweight piezoelectrics, with comparable or better piezoelectric response and superior me- chanical properties than in piezoelectric polymers. However, contrary to the conclusions of Ref. 7, our combined Berry phase and Wannier function ~WF! analysis demonstrates that electronic polarization in BNNT's does not change its direc- tion but rather grows monotonically with the increasing di- ameter of the tube. Furthermore, the electronic and ionic spontaneous polarizations in BNNT's cancel exactly and these systems are pyroelectric only if their intrinsic helical symmetry is broken by, e.g., intertube interactions or elastic distortions. The rest of this paper is organized as follows: Sec. II briefly reviews the formulation of the modern polarization theory in terms of Berry phases or Wannier functions. It also presents the details of the numerical techniques that were used to compute polarization. In Sec. III we discuss the re- sults and the complementary nature of the two techniques to compute the spontaneous polarization. Finally, Sec. IV pre- sents the summary and conclusions.

Subfields: Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/543d3f5403e4b66c0cc593fb88f84b521c0d14fe

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In Materials Chemistry

  1. P. Sharma
  2. N. Sharma
  3. R. Maranganti
  4. A. Tagantsev
  5. Q. Deng
  6. S. Shen
  7. Shuling Hu
  8. Liping Liu

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