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<p>The temperature dependence of the unit-cell parameters of synthetic Na(Mg<sub>0.5</sub>Si<sub>0.5</sub>)Si<sub>2</sub>O<sub>6</sub> clinopyroxene and Na<sub>2</sub>MgSi<sub>5</sub>O<sub>12</sub> garnet were measured, at atmospheric pressure, using X-ray powder diffraction, from 40&#xa0;K up to their decomposition temperatures (673&#xa0;K and 793&#xa0;K respectively). At 300&#xa0;K the cell parameters were found to be: (i) <i>a</i> = 9.4073(3) Å, <i>b</i> = 8.6487(3) Å, <i>c</i> = 5.2685(2) Å, <i>β</i> = 108.113(2)°, <i>V</i> = 407.41(3) Å<sup>3</sup> and <i>ρ</i> = 3.286&#xa0;g/cm<sup>3</sup>, for Na(Mg<sub>0.5</sub>Si<sub>0.5</sub>)Si<sub>2</sub>O<sub>6</sub> pyroxene in space-group <i>P2/n</i> with Z = 4 and (ii) <i>a</i> = 11.4155(7) Å, <i>V</i> = 1487.61(5) Å<sup>3</sup> and <i>ρ</i> = 3.561&#xa0;g/cm<sup>3</sup> for Na<sub>2</sub>MgSi<sub>5</sub>O<sub>12</sub> garnet in space-group <i>Ia</i><InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="269_2025_1315_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="10" /> </InlineMediaObject> <EquationSource Format="TEX">\(\overline{3}\)</EquationSource> <EquationSource Format="MATHML"><math> <mover> <mn>3</mn> <mo>¯</mo> </mover> </math></EquationSource> </InlineEquation><i>d</i> with Z = 8. The thermal expansion tensors have been calculated and analysis of the lattice parameters in terms of a Grüneisen-Debye model is used to estimate the Debye temperature and the incompressibility of the two materials at ambient pressure.</p>

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The thermal expansion of the clinopyroxene and garnet polymorphs of Na2MgSi5O12 determined by X-ray powder diffraction

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  • 发表日期：

    2025年4月2日

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  • E. K. Tripoliti,
  • A. R. Thomson,
  • D. P. Dobson,
  • P. F. Schofield,
  • I. G. Wood

摘要

The temperature dependence of the unit-cell parameters of synthetic Na(Mg0.5Si0.5)Si2O6 clinopyroxene and Na2MgSi5O12 garnet were measured, at atmospheric pressure, using X-ray powder diffraction, from 40 K up to their decomposition temperatures (673 K and 793 K respectively). At 300 K the cell parameters were found to be: (i) a = 9.4073(3) Å, b = 8.6487(3) Å, c = 5.2685(2) Å, β = 108.113(2)°, V = 407.41(3) Å3 and ρ = 3.286 g/cm3, for Na(Mg0.5Si0.5)Si2O6 pyroxene in space-group P2/n with Z = 4 and (ii) a = 11.4155(7) Å, V = 1487.61(5) Å3 and ρ = 3.561 g/cm3 for Na2MgSi5O12 garnet in space-group Ia \(\overline{3}\) 3 ¯ d with Z = 8. The thermal expansion tensors have been calculated and analysis of the lattice parameters in terms of a Grüneisen-Debye model is used to estimate the Debye temperature and the incompressibility of the two materials at ambient pressure.