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Local nm-Scale Imaging of Electrical Contact for Series Resistance Degradation of Silicon Solar Cells

We report on an electrical conduction mechanism for series resistance (Rs) degradation observed in a utility scale solar farm by nm-scale imaging of the local resistance at the Ag/Si interface of c-Si cell front metallization. Our previous work showed that the I-V measurement of individual cells demonstrated exclusively the cell Rs degradation, and the "beads pattern" of electroluminescence indicated the degradation at the Ag grid of front metallization. Scanning spreading resistance microscopy (SSRM) imaging, which is based on the contact mode of atomic force microscopy and taken on the cross-sections of Ag/Si contact, revealed the electrical conduction pathway of Ag particles in point or small area contact with Si cell emitter. The SSRM results illustrated that the number of electrical contacts in the degraded cell decreased largely compared with the unaffected cell, demonstrating the direct cause of the Rs degradation. This reduction in electrical contact in the degraded cell could be caused by a structural change in the Ag grid during long-term field service: The Ag particles in contact with Si aggregate into the Ag bulk and a highly resistive ceramic oxide is formed in a "belt" shape at the Ag/Si interface. This resistive belt with a thickness of ~1 m blocks the current conduction from cell emitter to the Ag grid. The degraded cell shows both a morphological and chemical difference in the screen-printed finger contact compared to the unaffected cell, which likely caused the different degradation susceptibility during the long-term field service. Our results demonstrate an example of the multi-scale characterization approach for understanding photovoltaic degradation mechanisms.

ENGINEERING,SOLAR ENERGY↗

Structure and Electronic Properties of Mesopores in Si PV Devices with PLEO Contacts

All current state-of-the-art silicon photovoltaic (PV) devices employ some flavor of passivating contact structure to minimize detrimental recombination while providing good conductivity. These properties are most often provided by a dielectric layer (SiNx, Al2O3, or SiOx) that is in contact with the crystalline silicon (c-Si) substrate. The effectiveness of these layers is heavily dependent on the nanoscale structure of both the dielectric layers and the crystalline silicon interface. As an example, the tunneling probability for charge carriers across thin SiOx layers, a process that is critical to maintain high conductivity, is extremely sensitive to the SiOx thickness. SiOx with a thickness below 2 nm readily allows charge carrier tunneling, whereas it is impeded for greater thicknesses. In the latter case it has been shown that modifications to the thermal processing schedule can induce disruptions, or pinholes, in thick SiOx layers that allow transport of charge carriers while maintaining excellent passivation. However, this requires higher temperatures processes that may inhibit widespread adoption by industry. Recently, another option has been presented that may circumvent the necessity for high temperature processing, namely metal assisted chemical etching (MACE). MACE relies on deposition of Ag nanoparticles onto the SiOx layers with subsequent electroless etching to form mesopores in the SiOx layers that are analogous to the pinholes created with high temperature processing. The size and density can be controlled based on the Ag nanoparticle deposition conditions. The resulting contact structure is known as polysilicon on locally etched oxide (PLEO) contacts. The nanoscale structure of the mesopores in PLEO contacts define the device level observables such as recombination current (Jo) and junction resistance. In this work we present atomic resolution transmission electron microscopy (TEM) analysis of mesopores in PLEO contacts formed with a different processing conditions to connect provide insight into how the nanoscale structure of the SiOx layer influences PV device properties. Additionally, we have previously used electron beam induced current (EBIC) to probe local transport properties in Si PV devices with a SiOx layer containing pinholes due to high temperature processing. Using EBIC we were able to directly show the enhance charge carrier transport through the pinholes. Here we also employ EBIC to study non-uniformities in charge carrier recombination and transport associated with mesopores in PLEO contacts and compare these results with our previous work on devices with pinholes in the SiOx formed through high temperature processes. The products of this work provide critical information that is required to both further optimize performance of Si PV devices with PLEO contact and to drive future adoption of this technology by industry.

ENGINEERING,SOLAR ENERGY↗

Research and Development Priorities for Silicon Photovoltaic Module Recycling to Support a Circular Economy

Large-scale deployment of photovoltaic (PV) modules has considerably increased in recent decades. Given an estimated lifetime of 30 years, the challenge of how to handle large volumes of end-of-life PV modules is starting to emerge. In this Perspective, we assess the global status of practice and knowledge for end-of-life management for crystalline silicon PV modules. We focus in particular on module recycling, a key aspect in the circular economy of photovoltaic panels. We recommend research and development to reduce recycling costs and environmental impacts compared to disposal while maximizing material recovery. We suggest that the recovery of high-value silicon is more advantageous than the recovery of intact silicon wafers. This approach requires the identification of contaminants and the design of purification processes for recovered silicon. The environmental and economic impacts of recycling practices should be explored with techno–economic analyses and life-cycle assessments to optimize solutions and minimize trade-offs. As photovoltaic technology advances rapidly, it is important for the recycling industry to plan adaptable recycling infrastructure.

c-Si↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are four inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. There are four inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.90 Å. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-4H structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. there are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are four inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. There are four inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.89 Å. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. there are four inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. There are four inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. there are five inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fifth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. There are five inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fifth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. there are five inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fifth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. There are five inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fifth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Si4+ is bonded to six equivalent C4- atoms to form a mixture of edge and corner-sharing SiC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Si–C bond lengths are 2.03 Å. C4- is bonded to six equivalent Si4+ atoms to form a mixture of edge and corner-sharing CSi6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. there are five inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the fifth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. There are five inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.89 Å. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fifth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. there are six inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fifth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the sixth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. There are five inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.89 Å. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fifth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. there are four inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. There are four inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.90 Å.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-4H-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are six inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fifth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the sixth Si4+ site, Si4+ is bonded to four equivalent C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. There are six inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.90 Å. In the third C4- site, C4- is bonded to four equivalent Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fifth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the sixth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.90 Å.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are four inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. There are four inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.90 Å.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. there are four inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. There are four inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.90 Å. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on SiC by Materials Project

SiC is Moissanite-6H-like structured and crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. there are five inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fifth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. There are five inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.90 Å. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.89 Å. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fifth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.

36 MATERIALS SCIENCE↗