The state of substances under ultrahigh pressures and temperatures (UHPHT) now raises a special interest as a matter existing under extreme conditions and as potential new material. Under laboratory conditions only small amounts of micrometer-sized matter are produced at a pressure up to 100 GPa and at room temperature. Simultaneous combination of ultrahigh pressures and temperatures in a lab still requires serious technological effort. Here we describe the composition and structure of the UHPHT vein-like impact glass discovered by us in 2015 on the territory of the Kara astrobleme (Russia) and compare its properties with impact glass from the Ries crater (Germany). A complex of structural and spectroscopic methods presents unusual high pressure marks of structural elements in 8-fold co-ordination that had been described earlier neither in synthetic nor natural glasses. The Kara natural UHPHT glasses being about 70 Ma old have well preserved initial structure, presenting some heterogeneity as a result of partial liquation and crystallization differentiation where an amorphous component is proposed to originate from low level polymerization. Homogeneous parts of the UHPHT glasses can be used to deepened fundamental investigation of a substance under extreme PT conditions and to technological studies for novel material creations.
The pyrochlore-type solid-solution
formation in a Bi1.6Mg0.8–x
Cu
x
Ta1.6O7.2−Δ system, synthesized
for the first time, is observed at x ≤ 0.56.
High-temperature X-ray diffraction showed that the pyrochlore phase
exists in air up to 1080 °C, where its thermal decomposition
leads to the segregation of (Mg,Cu)Ta2O6. The
thermal expansion coefficients of the end member, Bi1.6Mg0.24Cu0.56Ta1.6O7.2−Δ, increase from 3.3 × 10–6 °C–1 at room temperature up to 8.7 × 10–6 °C–1 at 930 °C. Rietveld refinement confirmed that
the pyrochlore crystal structure is disordered with space group Fd3̅m:2 (Z = 8,
no. 227). Doping with copper results in a modest expansion of the
cubic unit cell, promotes sintering of the ceramic materials, and
induces their red-brown color. X-ray photoelectron spectroscopy demonstrated
that the states of Bi(III) and Mg(II) are not affected by doping,
and the effective charge of tantalum cations is lower than +5, while
the Cu(II) states coexist with Cu(I). The electron spin resonance
spectra display a single line with g = 2.2, ascribed
to the dipole-broadened Cu2+ signal. The dielectric permittivity
of Bi1.6Mg0.8–x
Cu
x
Ta1.6O7.2−Δ ceramics may achieve up to ∼105, with the dielectric
loss tangent varying in the range from 0.2 up to 12. Multiple dielectric
relaxations are found at room temperature and above for all samples.
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