Lattice dynamics of andalusite: Prediction and experiment

Winkler, Bjoern; Buehrer, W.

doi:10.1007/bf00212215

Cited by 23 publications

(4 citation statements)

References 22 publications

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“…One possibility is that the peak at 690 cm −1 relates to stretching modes in five-fold-coordinated AlO 5 polyhedra. A significant absorption peak near 690 cm −1 has been observed by several authors for the aluminosilicate andalusite (Al 2 SiO 4 ) [235]- [237], in which Al is distributed equally between five-and six-fold coordinated sites (AlO 5 and AlO 6 ) [238]. This peak is not observed for the compositionally identical orthosilicates sillimanite and kyanite, which do not feature AlO 5 coordination [238].…”

Section: Al-o Bondsmentioning

confidence: 84%

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Black

2016

Springer Theses

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High-efficiency crystalline silicon solar cells must suppress recombination at their p-type surfaces. Thin-film, amorphous aluminium oxide (Al 2 O 3) has been shown to provide very effective passivation of such surfaces, assisted by its negative fixed charge. However, many details of Al 2 O 3 passivation remain poorly understood. Furthermore, conventional means of depositing passivating Al 2 O 3 are too slow or too expensive to be suitable for high-volume commercial production. This thesis addresses these issues in three ways: 1) by contributing to a deeper understanding of semiconductor-dielectric interfaces and semiconductor surface recombination mechanisms in general, 2) by investigating the properties of Al 2 O 3 as a passivating dielectric for silicon surfaces, and 3) by demonstrating the viability of APCVD as a high-throughput, industrially compatible deposition method for Al 2 O 3 , enabling its application to commercial solar cells. Using Al 2 O 3 as a test case, it is shown how a novel analysis of the extended conductance method can be used to i) distinguish the separate contributions to the interface state distribution at a semiconductor-dielectric interface, and ii) determine their capture cross-sections for both minority and majority carriers. Furthermore, the direct link between these measured interface state properties and the recombination rate at the semiconductor surface is experimentally demonstrated by showing that the former can be used to accurately predict the latter. Investigations of the surface passivation properties of Al 2 O 3 reveal a remarkably consistent picture. It is shown that the properties of the Si-Al 2 O 3 interface states are essentially independent of the Al 2 O 3 deposition conditions and technique. The interface properties are found to be independent of the surface dopant concentration at boron-and phosphorus-doped surfaces, while recombination is shown to be only weakly dependent on surface orientation and morphology as a result of the remarkable orientation-independence of the Si-Al 2 O 3 interface state properties. Meanwhile, the chemical origin of the charge at the Si-Al 2 O 3 interface is elucidated by correlating FTIR and electrical measurements. xi xii APCVD is clearly shown-for the first time-to be capable of depositing Al 2 O 3 films with exceptional surface passivation properties, comparable to the best results achieved using other deposition techniques. In the best case, interface state densities as low as 5 × 10 10 eV −1 cm −2 at midgap, and negative fixed charge concentrations of 3.3 × 10 12 cm −2 are measured, resulting in a saturation current density of 7 fA cm −2 on undiffused p-type surfaces. The APCVD films are shown to be thermally stable under standard solar cell processing conditions and are demonstrated in large-area solar cells with peak efficiencies of 21.3 %. These results demonstrate the viability of APCVD Al 2 O 3 as a surface passivation layer for industrial silicon solar cells.

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Section: Al-o Bondsmentioning

confidence: 84%

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Black

2016

Springer Theses

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“…71 The ambient phase of this framework structure contains four-coordinate Si atoms. 80 Lattice-dynamical calculations using well-established interaction potentials optimised for aluminosilicates 81 indicate that the framework undergoes a correlated reorganisation between 30 and 40 GPa that increases the Si coordination number from four to five. 71 All original bonding connectivity is preserved in this process (only new bonds are formed), and there is no change in crystal symmetry; such a transition is necessarily first-order in nature.…”

Section: Ferroelasticsmentioning

confidence: 99%

Negative linear compressibility

Cairns

Goodwin

2015

Phys. Chem. Chem. Phys.

240

341

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While all materials reduce their intrinsic volume under hydrostatic (uniform) compression, a select few actually expand along one or more directions during this process of densification. As rare as it is counterintuitive, such "negative compressibility" behaviour has application in the design of pressure sensors, artificial muscles and actuators. The recent discovery of surprisingly strong and persistent negative compressibility effects in a variety of new families of materials has ignited the field. Here we review the phenomenology of negative compressibility in this context of materials diversity, placing particular emphasis on the common structural motifs that recur amongst known examples. Our goal is to present a mechanistic understanding of negative compressibility that will help inform a clear strategy for future materials design.

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“…Here we use the simple ionic shell model, which proved to be suf®ciently good to describe the lattice dynamics of silicate minerals (Burnham, 1990), including the Al 2 SiO 5 polymorphs (Winkler & Buehrer, 1990;Rao et al, 1999). The total lattice energy is given by…”

Section: Semiclassical Calculationsmentioning

confidence: 99%

Theoretical investigation of metastable Al₂SiO₅polymorphs

2001

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Using theoretical simulations based on density functional theory within the generalized gradient approximation, a series of metastable phase transitions occurring in low-pressure Al 2 SiO 5 polymorphs (andalusite and sillimanite) are predicted; similar results were obtained using semiclassical interatomic potentials within the ionic shell model. Soft lattice modes as well as related structural changes are analysed. For sillimanite, an isosymmetric phase transition at ca 35 GPa is predicted; an incommensurately modulated form of sillimanite can also be obtained at low temperatures and high pressures. The high-pressure isosymmetric phase contains ®ve-coordinate Si and Al atoms. The origin of the ®vefold coordination is discussed in detail. Andalusite was found to transform directly into an amorphous phase at ca 50 GPa. This study provides an insight into the nature of metastable modi®cations of crystal structures and the ways in which they are formed. Present results indicate the existence of a critical bonding distance, above which interatomic interactions cannot be considered as bonding. The critical distance for the SiÐO bond is 2.25 A Ê .

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Lattice dynamics of andalusite: Prediction and experiment

Cited by 23 publications

References 22 publications

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Negative linear compressibility

Theoretical investigation of metastable Al₂SiO₅polymorphs

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Lattice dynamics of andalusite: Prediction and experiment

Cited by 23 publications

References 22 publications

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Negative linear compressibility

Theoretical investigation of metastable Al2SiO5polymorphs

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Theoretical investigation of metastable Al₂SiO₅polymorphs