High-Pressure Phase Diagrams of Na<sub>2</sub>CO<sub>3</sub> and K<sub>2</sub>CO<sub>3</sub>
oleh: Pavel N. Gavryushkin, Altyna Bekhtenova, Sergey S. Lobanov, Anton Shatskiy, Anna Yu. Likhacheva, Dinara Sagatova, Nursultan Sagatov, Sergey V. Rashchenko, Konstantin D. Litasov, Igor S. Sharygin, Alexander F. Goncharov, Vitali B. Prakapenka, Yuji Higo
| Format: | Article |
|---|---|
| Diterbitkan: | MDPI AG 2019-09-01 |
Deskripsi
The phase diagrams of Na<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula> and K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula> have been determined with multianvil (MA) and diamond anvil cell (DAC) techniques. In MA experiments with heating, <inline-formula> <math display="inline"> <semantics> <mi>γ</mi> </semantics> </math> </inline-formula>-Na<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula> is stable up to 12 GPa and above this pressure transforms to <inline-formula> <math display="inline"> <semantics> <mrow> <mi>P</mi> <msub> <mn>6</mn> <mn>3</mn> </msub> </mrow> </semantics> </math> </inline-formula>/<i>mcm</i>-phase. At 26 GPa, Na<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>-<inline-formula> <math display="inline"> <semantics> <mrow> <mi>P</mi> <msub> <mn>6</mn> <mn>3</mn> </msub> </mrow> </semantics> </math> </inline-formula>/<i>mcm</i> transforms to the new phase with a diffraction pattern similar to that of the theoretically predicted Na<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>-<inline-formula> <math display="inline"> <semantics> <mrow> <mi>P</mi> <msub> <mn>2</mn> <mn>1</mn> </msub> </mrow> </semantics> </math> </inline-formula>/<i>m</i>. On cold compression in DAC experiments, <inline-formula> <math display="inline"> <semantics> <mi>γ</mi> </semantics> </math> </inline-formula>-Na<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula> is stable up to the maximum pressure reached of 25 GPa. K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula> shows a more complex sequence of phase transitions. Unlike <inline-formula> <math display="inline"> <semantics> <mi>γ</mi> </semantics> </math> </inline-formula>-Na<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>, <inline-formula> <math display="inline"> <semantics> <mi>γ</mi> </semantics> </math> </inline-formula>-K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula> has a narrow stability field. At 3 GPa, K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula> presents in the form of the new phase, called K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>-III, which transforms into another new phase, K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>-IV, above 9 GPa. In the pressure range of 9−15 GPa, another new phase or the mixture of phases III and IV is observed. The diffraction pattern of K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>-IV has similarities with that of the theoretically predicted K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>-<inline-formula> <math display="inline"> <semantics> <mrow> <mi>P</mi> <msub> <mn>2</mn> <mn>1</mn> </msub> </mrow> </semantics> </math> </inline-formula>/<i>m</i> and most of the diffraction peaks can be indexed with this structure. Water has a dramatic effect on the phase transitions of K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>. Reconstruction of the diffraction pattern of <inline-formula> <math display="inline"> <semantics> <mi>γ</mi> </semantics> </math> </inline-formula>-K<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula> is observed at pressures of 0.5−3.1 GPa if the DAC is loaded on the air.