Abstract
It’s of great significance to explore the synthesis of tourmaline with simple chemical composition to study the mechanism of its pyroelectric properties due to the presence of crystal defects and isomorphous substitution in natural tourmaline. In the present work, dravite is firstly synthesized by high pressure solid-state method at 5-6 GPa and 550-650 °C. X-ray powder diffraction and electron microprobe analysis data indicate that the synthesized sample is the compound of the dravite with the formula of NaMg3Al6Si6B3O27(OH)4 and a small amount of SiO2. Compared with the natural dravite, the pyroelectric coefficient of the synthesized dravite is improved by an order of magnitude due to the great increase of the intrinsic dipole moment in synthesized dravite. The temperature dependent infrared spectra shows that the dipole moment of each ionic group in the synthesized dravite increases with temperature, leading to the raise of the pyroelectric coefficient with the increment of temperature. And in all ionic groups, [SiO4] tetrahedron and [BO3] triangle are the most important ionic groups that caused the pyroelectricity of tourmaline.
Highlights
IntroductionTourmaline is a kind of borosilicate mineral with good physical properties such as spontaneous polarization, pyroelectricity, infrared radiation and releasing negative ion characteristics
Tourmaline is a kind of borosilicate mineral with good physical properties such as spontaneous polarization, pyroelectricity, infrared radiation and releasing negative ion characteristics.1,2 Due to these characteristics, tourmaline can be used in various industries such as environmental protection, chemical industry and biomedicine.3–6 The general formula of tourmaline can be represented by XY3Z6[T6O18][BO3]3V3W, where usually X = Na+, K+, Ca2+ or a vacancy; Y = Mg2+, Al3+, Li+, Fe2+, Fe3+, Cr3+, Ti4+, Mn2+ and many other cations; Z = Al3+, Mg2+, Fe3+, Cr3+; T = Si4+, Al3+; B = B3+; V = OH, O2-; W = OH, F, O2-.7–9 According to our previous work, the tourmaline structure consists of six-membered rings of tetrahedra (T-sites)
The polycrystalline dravite NaMg3Al6Si6B3 O27(OH)4 with simple chemical composition has been firstly synthesized by high pressure solid-state method
Summary
Tourmaline is a kind of borosilicate mineral with good physical properties such as spontaneous polarization, pyroelectricity, infrared radiation and releasing negative ion characteristics.. Tourmaline is a kind of borosilicate mineral with good physical properties such as spontaneous polarization, pyroelectricity, infrared radiation and releasing negative ion characteristics.1,2 Due to these characteristics, tourmaline can be used in various industries such as environmental protection, chemical industry and biomedicine.. According to our previous work, the tourmaline structure consists of six-membered rings of tetrahedra (T-sites). The T-sites are occupied by Si. The rings of tetrahedra are linked to triangular BO3 groups (B-site), ninecoordinated X-sites, and two different octahedral sites, Y and Z. For each six-membered ring of tetrahedral, there are three B-sites, three Y-sites, six Z-sites and one X-site, as shown in Fig. 1 and Fig. 2.10
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