Indium Ammoniates from Ammonothermal Synthesis: InAlF6(NH3)2, [In(NH3)6][AlF6], and [In2F(NH3)10]2[SiF6]5 ∙ 2 NH3

Peter Becker,Rainer Niewa,Toni Boris Cekovski

doi:10.3390/cryst11060679

Abstract

The ammonothermal synthesis of three ammoniates of indium, namely InAlF6(NH3)2, [In(NH3)6][AlF6], and [In2F(NH3)10]2[SiF6]5 ∙ 2 NH3 was successful from near-ammononeutral conditions in the presence of fluoride ions. Initially, all these compounds were obtained upon corrosion of the applied liner and crucible material Si3N4, which also contains small amounts of aluminum. The syntheses were performed in supercritical ammonia (T = 753 K, p up to 307 MPa). The crystal structures were solved and refined from single crystal X-ray diffraction intensity data. InAlF6(NH3)2 crystallizes as a typical layer-type structure with corner-sharing [InF4(NH3)2]– and [AlF6]3− octahedra. [In(NH3)6][AlF6] features isolated [In(NH3)6]3+ and [AlF6]3− octahedra. The crystal structure of [In2F(NH3)10]2[SiF6]5 ∙ 2 NH3 contains [(NH3)5In–F–In(NH3)5]5+ octahedra doubles next to [SiF6]2− octahedra and ammonia molecules. All intermediates have strong hydrogen bonding systems. The results from vibrational spectroscopy are reported.

Highlights

Huge efforts into the investigation of group III nitrides have been made because of their wide application in electronic devices, such as light-emitting diodes and lasers [1]
Intermediates, which form during near-ammononeutral InN synthesis can be obtained by reacting indium trihalides together with three molar equivalents of an alkali metal amide
The presence of aluminum in the Si3N4 material was proven by wavelength dispersive X-ray spectroscopy (WDS)

Summary

Introduction

Huge efforts into the investigation of group III nitrides have been made because of their wide application in electronic devices, such as light-emitting diodes and lasers [1]. The ammonothermal synthesis route is especially useful for the synthesis of high-quality free-standing crystals of group III nitrides [7,8,9,10]. These materials can be employed, for instance, as substrates in hydride vapor phase epitaxy (HVPE), which enables fast growth rates and high purity coupled with high structural quality [11]. It was demonstrated that it is possible to synthesize InN crystals with sizes in the micrometer range [13] During such reactions, so-called mineralizers are used in order to enhance the solubility of the starting materials. Since InN is highly corrosive against nickel-based alloys, which are typically used for ammonothermal syntheses, ceramic liners from Si3N4 or BN are employed to protect the autoclave [14]

Methods

Results

Conclusion