An extension of the Czjzek model for the distributions of electric field gradients in disordered solids and an application to NMR spectra of 71Ga in chalcogenide glasses.

Journal of physics. Condensed matter : an Institute of Physics journal · 2010 · Unclear · Insufficient evidence

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UnclearInsufficient evidencePaper 3309

Study snapshot

PublicationJournal of physics. Condensed matter : an Institute of Physics journal · 2010

Study typeother

Reported directionUnclear

Evidence ratingInsufficient

Abstract

First, the basis and the characteristics of the Czjzek model for the distribution of electric field gradient (EFG) tensor in disordered solids, some of which are still unnoticed, are depicted. That model results from the statistical invariance by rotation of the structure of the considered disordered solid and from the applicability of a central limit theorem to the EFG tensor. These two conditions, which are physically realistic for a wealth of disordered solids, simplify tremendously the derivation of the EFG distribution but at the cost of a complete loss of structural information about the investigated solid. Next, we describe a simple extension of it which is intended to mimic a well-defined local environment, with given values of the asymmetry parameter and of the principal component Vzz of the EFG tensor, perturbed by the disorder of more remote atoms. The effect of disorder is rendered by a Gaussian (Czjzek) noise with an adjustable weight relative to Vzz. The number of free parameters is limited to three, as compared to a sole scale factor for the Czjzek model. Its characteristics are described as a function of the given asymmetry parameter and of the strength of the noise. The aim is to lead to a practical tool which may help to retrieve, as far as possible, the information about the local environment perturbed by disorder from hyperfine measurements and notably from NMR spectra of quadrupolar nuclei. As an example, that extension is applied to some static NMR spectra of 71Ga in covalent glasses. Calculated static 71Ga NMR lineshapes are shown as a function of the parameters of the extended model.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typeother

Effect directionunclear

PopulationNot supplied

Sample sizeNot supplied

ExposureNot supplied

Evidence strengthInsufficientConfidence: 74% · Peer reviewed: yes

Main findings

The paper describes characteristics of the Czjzek model for EFG tensor distributions in disordered solids and proposes an extension that represents a defined local environment (specified asymmetry parameter and Vzz) perturbed by Gaussian (Czjzek) noise with adjustable weight. The extended model uses three free parameters and is applied to static 71Ga NMR spectra in covalent glasses, showing calculated lineshapes as a function of model parameters.

Outcomes measured

Electric field gradient (EFG) tensor distribution modeling in disordered solids
Extension of the Czjzek model to include a defined local environment plus Gaussian (Czjzek) noise
Application to calculated/static 71Ga NMR lineshapes in chalcogenide/covalent glasses

Limitations

No health/biological outcomes are described in the abstract
No sample size or experimental design details are provided in the abstract
Results are presented as model characteristics and calculated NMR lineshapes; empirical validation details are not stated in the abstract

View raw extracted JSON

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  "study_type": "other",
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  },
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  "outcomes": [
    "Electric field gradient (EFG) tensor distribution modeling in disordered solids",
    "Extension of the Czjzek model to include a defined local environment plus Gaussian (Czjzek) noise",
    "Application to calculated/static 71Ga NMR lineshapes in chalcogenide/covalent glasses"
  ],
  "main_findings": "The paper describes characteristics of the Czjzek model for EFG tensor distributions in disordered solids and proposes an extension that represents a defined local environment (specified asymmetry parameter and Vzz) perturbed by Gaussian (Czjzek) noise with adjustable weight. The extended model uses three free parameters and is applied to static 71Ga NMR spectra in covalent glasses, showing calculated lineshapes as a function of model parameters.",
  "effect_direction": "unclear",
  "limitations": [
    "No health/biological outcomes are described in the abstract",
    "No sample size or experimental design details are provided in the abstract",
    "Results are presented as model characteristics and calculated NMR lineshapes; empirical validation details are not stated in the abstract"
  ],
  "evidence_strength": "insufficient",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "Czjzek model",
    "electric field gradient",
    "disordered solids",
    "Gaussian noise",
    "asymmetry parameter",
    "Vzz",
    "hyperfine measurements",
    "NMR",
    "quadrupolar nuclei",
    "71Ga",
    "chalcogenide glasses",
    "covalent glasses"
  ],
  "suggested_hubs": []
}

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Identifiers and source

DOI: 10.1088/0953-8984/22/6/065402
PubMed: 21389367

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