Defect physics in complex energy materials

Hoang, Khang; Johannes, M. D.

doi:10.1088/1361-648x/aacb05

Cited by 51 publications

(66 citation statements)

References 161 publications

(531 reference statements)

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“…Exploiting the structural complexity of crystalline materials is a powerful strategy for designing novel materials [1]. For instance, it allows disentangling electronic and heat transport which is of significant interest in the field of thermoelectricity [2,3,4,5].…”

Section: Introductionmentioning

confidence: 99%

Isostructural phase transition by point defect reorganization in the binary type-I clathrate Ba7.5Si45

Debord¹,

Euchner²,

Pischedda³

et al. 2021

Acta Materialia

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Competition between point defect (vacancy and interstitial) microscopic configurations is inherent to crystalline phases of increased structural complexity. Phase transitions that preserve symmetry between them belong to a specific class of isostructural transitions. Type-I silicon clathrates are complex crystalline phases whose unit cell containing fifty atoms consists of a 3D covalent silicon framework of face-sharing polyhedral cages encapsulating guest cations.At high pressure, an intriguing structural transition is associated with an abrupt reduction of volume with no indication for any breakage of symmetry. Using isothermal high-pressure Xray diffraction performed on a single crystal of the simplest representative type-I silicon clathrates, binary Ba8Si46, we confirm the isostructural character of the transition and identify the associated mechanism. A detailed analysis of the atomic structural parameters across the transition in combination with ab initio studies allow us to pinpoint a microscopic mechanism driven by a rearrangement of point defects initially present in the structure. An analysis based on the Landau theory gives a coherent description of the experimental observations. A discussion on the analogy between this transformation and liquid-liquid transitions is proposed.

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Section: Introductionmentioning

confidence: 99%

Isostructural phase transition by point defect reorganization in the binary type-I clathrate Ba7.5Si45

Debord¹,

Euchner²,

Pischedda³

et al. 2021

Acta Materialia

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“…Overall, defect formation is determined by the electronic structure, as it has also been discussed in other classes of materials [36]. Through a careful examination and detailed discussion of the electronic structure of Ln-doped GaN, we explain why certain Ln Ga defect configurations can be stabilized in GaN while others cannot.…”

Section: Electronic Structurementioning

confidence: 73%

Rare-earth defects in GaN: A systematic investigation of the lanthanide series

Hoang

2022

Preprint

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Rare-earth (RE) doped GaN is of interest for optoelectronics and spintronics and potentially for quantum applications. A fundamental understanding of the interaction between RE dopants and the semiconductor host is key to realizing the material's full potential. This work reports an investigation of lanthanide (Ln) defects in GaN using hybrid density-functional defect calculations. We find that all the Ln dopants incorporated at the Ga lattice site, LnGa (Ln = La-Lu), are stable as trivalent ions, but Eu and Yb can also be stabilized as divalent and Ce, Pr, and Tb as tetravalent. The location of Ln-related defect energy levels and of the Ln 4f states in the energy spectrum of the host material is determined from first principles. We elucidate the interplay between defect formation and electronic structure, including the Ln-N interaction, and the effect of doping on the local lattice environment. Optical properties are investigated by considering possible band-to-defect and defect-to-band transitions involving the LnGa defects. These "charge-transfer" transitions result in broad absorption and emission bands which likely impact the performance of the material.

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“…11(a) of Ref. 20. Also note that, even with co-doping, one still need to suppress the formation of oxygen vacancies and the Ba-site occupancy (see above), otherwise V 2+ O and/or Dy + Ba will counteract the effect of co-doping.…”

Section: (Co-)doping With Yttriummentioning

confidence: 98%

“…Given the above results and discussion, one may expect that Dy exists entirely or predominantly as the trivalent Dy 3+ (i.e., Dy − Zr ) in BaZrO 3 under normal synthesis conditions, and Dy − Zr is charge-compensated predominantly by V 2+ O and/or Dy + Ba . The native and RE-related defects, once formed or incorporated during the synthesis reaction, are expected to remain trapped in the material after the synthesis and act as athermal, prexisting defects in subsequent experiments [20]. We refer to BaZrO 3 at this stage as being as-synthesized.…”

Section: Post-synthesis Treatmentmentioning

confidence: 99%

Why is it so difficult to realize Dy$^{4+}$ in as-synthesized BaZrO$_3$?

Hoang,

Latouche,

Jobic

2021

Preprint

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Rare-earth doped barium zirconate (BaZrO3) ceramics are of interest as proton-conducting and luminescent materials. Here, we report a study of dysprosium (Dy) and other relevant point defects in BaZrO3 using hybrid density-functional defect calculations. The tetravalent Dy 4+ is found to be structurally and electronically stable at the Zr lattice site (i.e., as Dy 0 Zr ), but often energetically less favorable than the trivalent Dy 3+ (i.e., Dy − Zr ) in as-synthesized BaZrO3, due to the formation of low-energy, positively charged oxygen vacancies and the mixed-site occupancy of Dy in the host lattice. The Dy 4+ /Dy 3+ ratio can, in principle, be increased by preparing the material under highly oxidizing and Ba-rich conditions and co-doping with acceptor-like impurities; however, postsynthesis treatment may still be needed to realize a non-negligible Dy 4+ concentration. We also find that certain unoccupied Dy 4f states and the O 2p states are strongly hybridized, a feature not often seen in rare-earth-containing materials, and that the isolated DyZr defect might be the source of a broad blue emission in band-to-defect luminescence.

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Defect physics in complex energy materials

Cited by 51 publications

References 161 publications

Isostructural phase transition by point defect reorganization in the binary type-I clathrate Ba7.5Si45

Isostructural phase transition by point defect reorganization in the binary type-I clathrate Ba7.5Si45

Rare-earth defects in GaN: A systematic investigation of the lanthanide series

Why is it so difficult to realize Dy$^{4+}$ in as-synthesized BaZrO$_3$?

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