Polytypism in mcalpineite: a study of natural and synthetic Cu₃TeO₆

Abstract

Synthetic and naturally occurring forms of tricopper orthotellurate, CuII 3TeVIO6 (the mineral mcalpineite) have been investigated by 3D electron diffraction (3D ED), X-ray powder diffraction (XRPD), Raman and infrared (IR) spectroscopic measurements. As a result of the diffraction analyses, CuII 3TeVIO6 is shown to occur in two polytypes. The higher-symmetric CuII 3TeVIO6-1C polytype is cubic, space group Ia 3, with a = 9.537 (1) Å and V = 867.4 (3) Å3 as reported in previous studies. The 1C polytype is a well characterized structure consisting of alternating layers of CuIIO6 octahedra and both CuIIO6 and TeVIO6 octahedra in a patchwork arrangement. The structure of the lower-symmetric orthorhombic CuII 3TeVIO6-2O polytype was determined for the first time in this study by 3D ED and verified by Rietveld refinement. The 2O polytype crystallizes in space group Pcca, with a = 9.745 (3) Å, b = 9.749 (2) Å, c = 9.771 (2) Å and V = 928.3 (4) Å3. High-precision XRPD data were also collected on CuII 3TeVIO6-2O to verify the lower-symmetric structure by performing a Rietveld refinement. The resultant structure is identical to that determined by 3D ED, with unit-cell parameters a = 9.56157 (19) Å, b = 9.55853 (11) Å, c = 9.62891 (15) Å and V = 880.03 (2) Å3. The lower symmetry of the 2O polytype is a consequence of a different cation ordering arrangement, which involves the movement of every second CuIIO6 and TeVIO6 octahedral layer by (1/4, 1/4, 0), leading to an offset of TeVIO6 and CuIIO6 octahedra in every second layer giving an ABAB* stacking arrangement. Syntheses of CuII 3TeVIO6 showed that low-temperature (473 K) hydrothermal conditions generally produce the 2O polytype. XRPD measurements in combination with Raman spectroscopic analysis showed that most natural mcalpineite is the orthorhombic 2O polytype. Both XRPD and Raman spectroscopy measurements may be used to differentiate between the two polytypes of CuII 3TeVIO6. In Raman spectroscopy, CuII 3TeVIO6-1C has a single strong band around 730 cm−1, whereas CuII 3TeVIO6-2O shows a broad double maximum with bands centred around 692 and 742 cm−1.

Shape-Controlled Synthesis of Cu3TeO6 Nanoparticles with Photocatalytic Features

“…However, the samples also show a characteristic diffraction peak at 2θ = 24.24° corresponding to the characteristic peak of (210) of mineral mcalpineite “Cu 3 TeO 6 × H 2 O”. This fact indicates that the CTO synthesized by hydrothermal methodology presents both phases due to the aqueous environment which allows for the incorporation of water molecules in the crystal structure of Cu 3 TeO 6 as previously reported in the literature . Moreover, the crystallite sizes of the MTOs synthesized at different pH values were calculated using the Scherrer equation.…”

“…This fact indicates that the CTO synthesized by hydrothermal methodology presents both phases due to the aqueous environment which allows for the incorporation of water molecules in the crystal structure of Cu 3 TeO 6 as previously reported in the literature. 36 Moreover, the crystallite sizes of the MTOs synthesized at different pH values were calculated using the Scherrer equation. The results indicate that upon acidic conditions (pH = 4) a bigger crystallite grain size (76.2 nm) was formed while the CTO synthesized at higher (basic) pH such as pH = 6, pH = 8, and pH = 10 had crystallite grain sizes of 30.1 26.4, and 29.7 nm, respectively.…”

Crystal structure and investigation of Bi2TeO6·nH2O (0 ≤ n ≤ $${\raise0.5ex\hbox{$\scriptstyle 2$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle 3$}}$$): natural and synthetic montanite

“…Scans were taken from 400 to 4000 cm −1 , with the transmittance recorded every 2 cm −1 . These spectra clearly showed the broad main tellurate vibrational band centred at 634 cm −1 , the dominant feature of the pattern (consistent with the location of tellurate IR bands in minerals such as mcalpineite-2O (also 634 cm −1 ); Missen et al 2022). Tellurate bending modes were not visible as they occur at energies below 400 cm −1 .…”

Charge Storage Performance of Cubic Cu3TeO6 Nanoparticles for Supercapattery Application

“…The peak observed at 515 cm −1 corresponds to Cu−O bonds. 25,44 The IR, Raman, and XRD analyses confirm the formation of pure Cu 3 TeO 6 . The Cu 3 TeO 6 sample is subjected to TGA under nitrogen atmosphere.…”

“…The cubic structure of the synthesized Cu 3 TeO 6 nanoparticles is confirmed by XRD analysis. 21,25 Figure 1 shows the XRD pattern of a highly crystalline and pure Cu 3 TeO 6 sample obtained from a green amorphous precursor. Some of the intense 2θ reflections of the crystalline Cu 3 TeO 6 are at 18.7°, 32.6°, 37.8°, 54.5°, and 64.9°w ith corresponding ( 200), ( 222), ( 400), (440), and (622) planes, respectively.…”