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Equation 8 · Materials Discovery and Degradation in Practice: An Advanced Technical Guide

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RwpR_{wp}

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RwpR_{wp}

Symbol R_wp

the low.

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subscript

subscript

The lower label selects a particular version, component, or indexed member of the quantity. For example, x₀ and xₜ can be values at different positions.

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The honest summary: XRD tells you what phases are present and roughly how much of each, averaged over a macroscopic volume, with a precision that depends on how carefully the refinement was checked against chemistry. TEM tells you what a specific, small region actually looks like in real space, with a representativeness that depends entirely on where the sample happened to come from. A single instrument’s output presented as “the structure” of a new material, without the other, is an incomplete claim — and an increasingly common failure mode in less careful reporting is quoting a Rietveld RwpR_{wp} as if it were proof of phase purity, when it is a statement about fit quality against one assumed…
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The honest summary: XRD tells you what phases are present and roughly how much of each, averaged over a macroscopic volume, with a precision that depends on how carefully the refinement was checked against chemistry. TEM tells you what a specific, small region actually looks like in real space, with a representativeness that depends entirely on where the sample happened to come from. A single instrument’s output presented as “the structure” of a new material, without the other, is an incomplete claim — and an increasingly common failure mode in less careful reporting is quoting a Rietveld RwpR_{wp} as if it were proof of phase purity, when it is a statement about fit quality against one assumed model.

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