Superconductivity often emerges in the proximity of, or in competition with, symmetry-breaking ground states such as antiferromagnetism or charge density waves15 (CDW). A number of materials in the ...cuprate family, which includes the high transition-temperature (high-Tc) superconductors, show spin and charge density wave order.
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The ammonium analogues of the high-pressure potassium-bearing silicate phases K-hollandite, K-Si-wadeite, K-cymrite, and phengite were synthesized in the system (NH4)2O(-MgO)-Al2O3-SiO2-H2O N(M)ASH ...using multi-anvil and piston-cylinder equipment. Syntheses included NH4-hollandite (NH4AlSi3O8) at 12.3 GPa, 700°C; NH4-Si-wadeite (NH4)2Si4O9 at 10 GPa, 700°C; NH4-cymrite (NH4AlSi3O8·H2O) at 7.8 GPa, 800°C; and NH4-phengite NH4(Mg0.5Al1.5)(Al0.5Si3.5)O10(OH)2 at 4 GPa, 700 °C. Run products were characterized by SEM, FTIR, and powder XRD with Rietveld refinements. Cell parameters of the new NH4 end-members are: a = 9.4234(9) Å, c = 2.7244(3) Å, V = 241.93(5) Å3 (NH4-hollandite); a = 6.726(1) Å, c = 9.502(3) Å, V = 372.3(1) Å3 (NH4-Si-wadeite); a = 5.3595(3) Å, c = 7.835(1) Å, V = 194.93(5) Å3 (NH4-cymrite). NH4-phengite consisted of a mixture of 1M, 2M1, 2M2, 3T, and 2Or polytypes. The most abundant polytype, 2M1, has cell dimensions a = 5.2195(9) Å, b = 9.049(3) Å, c = 20.414(8) Å, β = 95.65(3)°, V = 959.5(5) Å3. All unit-cell volumes are enlarged in comparison to the potassium analogues. Substitution of NH4 for K does not cause changes in space group. NH4 incorporation was confirmed by the appearance of NH4-vibration modes ν4 and ν3 occurring in the ranges of 1397-1459 and 3223-3333 cm-1, respectively. Ammonium in eclogite facies metasediments is mainly bound in micas and concentrations may reach up to a few thousand parts per million. It can be stored to greater depths in high-pressure potassium silicates during ongoing subduction. This possibly provides an important mechanism for nitrogen and hydrogen transport into the deeper mantle.
The thermal behaviour of Ln(C.sub.3H.sub.7CO.sub.2).sub.3 (Ln = Er, Tm, Yb or Lu) was studied in argon from room temperature by means of thermogravimetry and differential thermal analysis up to 1400 ...°C, by infrared spectroscopy, hot-stage optical microscopy and X-ray diffraction. Melting prior to decomposition was observed in all four compounds, but its course depends on the rare-earth element. Decomposition to sesquioxides proceeds via the formation of dioxymonocarbonates (Ln.sub.2O.sub.2CO.sub.3) and release of 4-heptanone (C.sub.3H.sub.7COC.sub.3H.sub.7) as well as carbon dioxide (CO.sub.2) without evidence for an intermediate oxobutanoate stage. During the decomposition of Ln.sub.2O.sub.2CO.sub.3 into the respective sesquioxides (Ln.sub.2O.sub.3), an intermediate plateau extending from approximately 550 to 850 °C appears in the TG traces. The overall composition during this stage corresponds approximately to Ln.sub.2O.sub.2.8(CO.sub.3).sub.0.2, but the state is more probably a mixture of Ln.sub.2O.sub.2CO.sub.3 and Ln.sub.2O.sub.3. The stability of this intermediate state seems to decrease with the mass of the rare-earth elements. Complete conversion to Ln.sub.2O.sub.3 is reached at about 1100 °C. The overall thermal decomposition behaviour of the title compounds is different from previous reports for other rare-earth butanoates.
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•The thermal decomposition of cerium butanoate, pentanoate and hexanoate has been studied in Ar.•All compounds present transitions including melting prior to decomposition.•Gas release in the molten ...state results in irregular mass loss.•CO2 and symmetrical ketones are the main evolving gas species.•Ce2O(CnH2n+1CO2)4 and Ce2O2CO3 intermediate are detected before CeO2 formation.
The thermal behavior and decomposition of Ce-butanoate monohydrate (Ce(C3H7CO2)3·H2O), Ce-pentanoate (Ce(C4H9CO2)3) and Ce-hexanoate (Ce(C5H11CO2)3) were studied in a flow of argon while heating at 5°C/min. By means of several techniques such as simultaneous TG-DTA, FTIR evolved gas analysis, in-situ x-ray diffraction using a synchrotron source and hot-stage microscopy, it was found that all three compounds undergo melting transitions prior to decomposition and that decomposition involves intermediate stages including at least a Ce2O(CnH2n+1CO2)4 intermediate (n=3, 4 or 5 for Ce-butanoate, pentanoate or hexanoate respectively). The final decomposition product consists of CeO2, which is formed through a Ce-oxycarbonate. The Ce3+→Ce4+ oxidation seems to proceed via Ce2O3 that first results from the decomposition of the oxycarbonate phase. During the whole decomposition process, the evolved gas species consist of CO2 and symmetrical ketones.
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•Yttrium(III) isovalerate Y(C4H9CO2)3 was prepared and characterized.•Y(C4H9CO2)3 does not melt between 40°C and 110°C prior to decomposition.•Decomposition occurs at a 20°C higher temperature than ...for Yttrium(III) valerate.•CO2 and C9H18 (2,6-dimethyl-4-heptanone) are released during the decomposition.•The decomposition of Y(C4H9CO2)3 to Y2O3 proceeds through Y2O2CO3.
The thermal behaviour of yttrium(III) isovalerate (Y(C4H9CO2)3) was studied in argon by means of thermogravimetry, differential thermal analysis, FTIR-spectroscopy, hot-stage optical microscopy and X-ray diffraction with a laboratory Cu-tube source as well as with a synchrotron radiation source. Two structural transitions take place in the solid state at 100°C and 140°C. They are followed by the decomposition of the isovalerate salt with release of gaseous products consisting of CO2 and 2,6-dimethyl-4-heptanone and formation of Y2O2CO3 between 320°C and 440°C. Above 440°C, Y2O2CO3 is slowly converted to Y2O3 with release of CO2. The decomposition is complete at about 900°C.
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The thermal behaviour of Ln(C
3
H
7
CO
2
)
3
(Ln = Er, Tm, Yb or Lu) was studied in argon from room temperature by means of thermogravimetry and differential thermal analysis up to 1400 °C, by ...infrared spectroscopy, hot-stage optical microscopy and X-ray diffraction. Melting prior to decomposition was observed in all four compounds, but its course depends on the rare-earth element. Decomposition to sesquioxides proceeds via the formation of dioxymonocarbonates (Ln
2
O
2
CO
3
) and release of 4-heptanone (C
3
H
7
COC
3
H
7
) as well as carbon dioxide (CO
2
) without evidence for an intermediate oxobutanoate stage. During the decomposition of Ln
2
O
2
CO
3
into the respective sesquioxides (Ln
2
O
3
), an intermediate plateau extending from approximately 550 to 850 °C appears in the TG traces. The overall composition during this stage corresponds approximately to Ln
2
O
2.8
(CO
3
)
0.2
, but the state is more probably a mixture of Ln
2
O
2
CO
3
and Ln
2
O
3
. The stability of this intermediate state seems to decrease with the mass of the rare-earth elements. Complete conversion to Ln
2
O
3
is reached at about 1100 °C. The overall thermal decomposition behaviour of the title compounds is different from previous reports for other rare-earth butanoates.
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•The dehydration of La(C3H7CO2)3·xH2O takes place between 50°C and 120°C.•La(C3H7CO2)3 melts at 180°C.•The decomposition of La(C3H7CO2)3 to La2O2CO3 involves a meta-butyrate intermediate.•CO2 and ...C3H7COC3H7 (4-heptanone) are released between 250°C and 350°C.•La2O3 is formed as a final decomposition product.
The thermal decomposition of La(C3H7CO2)3·xH2O (x≈0.82) was studied in argon during heating at 5K/min. After the loss of bound H2O, the anhydrous butyrate presents at 135°C a phase transition to a mesophase, which turns to an isotropic liquid at 180°C. The decomposition of the anhydrous butyrate is associated to a solidification process. The final decomposition to La2O3 takes place via two intermediate products: La2O(C3H7CO2)4 and La2O2CO3 with release of CO2 and the symmetrical ketone C3H7COC3H7.
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The shifts in wavenumber of the ν3(SiO4) (approximately 1008 cm-1) Raman band of fully crystalline synthetic zircon with changing pressure (P) and temperature (T) were calibrated for application as a ...Raman spectroscopic pressure sensor in optical cells to about 1000 °C and 10 GPa. The relationship between wavenumber (ν) of this band and T from 22 to 950 °C is described by the equation ν (cm-1) = 7.54·10-9·T3 - 1.61·10-5·T2 - 2.89·10-2·T + 1008.9, where T is given in °C. The pressure dependence is nearly linear over the studied range in P. At approximately 25 °C, the θν/θP slope to 6.6 GPa is 5.69 cm-1/GPa, and that to 2 GPa is 5.77 cm-1/GPa. The θν/θP slope does not significantly change with temperature, as determined from experiments conducted along isotherms up to 700 °C. Therefore, this pressure sensor has the advantage that a constant θν/θP slope of 5.8 ± 0.1 cm-1/GPa can be applied in experiments to pressures of at least about 6.6 GPa without introducing a significant error. The pressure sensor was tested to determine isochores in experiments with H2O+Na2Si3O7 and H2O+NaAlSi3O8 fluids to 803 °C and 1.65 GPa. These pressures were compared to pressures calculated from the equation of state (EoS) of H2O based on the measured vapor dissolution or ice melting temperature for the same experiment. Pressures determined from the zircon sensor in runs in which NaAlSi3O8 melt dissolved in aqueous fluid were close to or lower than the pressure calculated from the EoS of H2O using the vapor dissolution or ice melting temperature. In experiments with H2O+Na2O+SiO2 fluids, however, the pressure obtained from the Raman spectrum of zircon was often significantly higher than that estimated from the EoS of H2O. This suggests that the pressures along some critical curves of water-silicate melt pseudobinary systems should be revised.
•Thermal decomposition of Yttrium 2-methylbutyrate in argon.•Yttrium 2-methylbutyrate (Y(C4H9CO2)3 was prepared and characterized.•Y(C4H9CO2)3 undergoes solid-solid phase transitions but doesn’t ...melt.•Decomposition occurs at a 75 °C higher temperature than for Yttrium 3-methylbutyrate.•CO2, 3,5-dimethyl-4-heptanone and an alkyne are released during the decomposition.•The decomposition of Y(C4H9CO2)3 to Y2O3 proceeds via Y2O2CO3.
The thermal decomposition of yttrium 2-methylbutyrate (Y(C4H9CO2)3) under argon gas flow has been investigated by means of simultaneous thermogravimetry and differential thermal analysis, FTIR-spectroscopy (solid residue and evolved gas analysis), mass spectrometry, hot-stage optical microscopy and X-ray diffraction with a standard laboratory Cu-tube source as well as with a high-energy synchrotron radiation source. At least one structural transition occurs in the solid state between 100 °C and 160 °C. The decomposition of the Y 2-methylbutyrate salt takes place above 400 °C. A first stage results in the formation of Y2O2CO3 between 400 °C and 490 °C. This decomposition step is accompanied by the release of CO2, a symmetrical ketone (3,5-dimethyl-4-heptanone), as well as probably a terminal alkyne, which could not be unambiguously identified. At higher temperature, Y2O2CO3 is slowly converted to Y2O3 with release of CO2, while some carbonaceous residue is eliminated via combustion. The TG trace reaches the final plateau at about 1200 °C.
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•The thermal decomposition of Lathanum valerate and caproate has been studied in Ar.•The compounds melt prior to decomposition.•Gas release in the molten state results in irregular ...mass loss.•CO2 and symmetrical ketones are the main evolving gas species.
The decomposition of La-valerate (La(C4H9CO2)3·xH2O (x≈0.45)) and La-caproate (La(C5H11CO2)3·xH2O (x≈0.30)) was studied upon heating at 5°C/min in a flow of argon. Using a variety of techniques including simultaneous TG-DTA, FTIR, X-ray diffraction with both laboratory Cu Kα and synchrotron sources as well as hot-stage microscopy, it was found that both compounds melt prior to decomposition and that the main decomposition stage from the molten, anhydrous state leads to the formation of La-dioxycarbonate (La2O2CO3) via an unstable intermediate product and release of symmetrical ketones. Final decomposition to La2O3 takes place with release of CO2.
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