Phosphate structure and lithium environments in lithium phosphorus oxynitride amorphous thin films

Abstract

International audienceLithium ion-conducting glasses attract wide interest for electrochemical applications like efficient energy storage devices. This work presents a structural study on involved bonding units, based on X-ray photoelectron spectroscopy and infrared spectroscopy, of lithium phosphorus oxide and oxynitride amorphous thin films prepared by RF magnetron sputtering. A thorough consideration of the mid- and far-infrared spectral regions demonstrated structural changes at the phosphate units and the lithium ion environments triggered by nitrogen incorporation and post-deposition thermal treatment. It was found that films prepared by sputtering in pure nitrogen atmosphere have about 75 % of their nitrogen atoms in sites doubly coordinated with phosphorus (P–N=P), and the rest in triply coordinated sites. It was shown also that nitrogen incorporation favors the stability of lithium ions, while annealing enhances ionic conductivity of the oxynitride films

Resolving the Amorphous Structure of Lithium Phosphorus Oxynitride (Lipon)

“…For the final change at about 1190 cm –1 , there could potentially be different modes involved, as the shoulder in the amorphous Li 3 PO 4 film mostly disappears, but the film with the highest N:O content also has an increased intensity relative to the other Lipon films. Previous work suggests that absorption around 1190 cm –1 in the pure oxide is due to the stretching of pyro-phosphate PO 3 groups, which would imply the presence of O b . Although we cannot exclude this possibility, since O b is seldom found in our modeled Lipon structures and is completely absent in the amorphous Li 3 PO 4 structure generated via AIMD, we will not follow such assignment.…”

“…For instance, Wang et al also observed XPS peaks in polycrystalline Li 2.88 PO 3.73 N 0.14 at binding energies 397.8 and 399.7 eV but assigned them differently based on the support of X-ray diffraction and chromatography data revealing the presence of nonbridging or apical N (N a ) along with a minor portion of N d due to some Li–P disorder. Infrared (IR) spectroscopy, Raman spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy of amorphous Lipon and related materials have also been collected, ,− but their interpretations have assumed the above-mentioned structural hypothesis proposed by Bates et al is correct; thus, the identification of N-related modes that might solve this discrepancy also remain inconclusive.…”

Structural impact of nitrogen incorporation on properties of alkali germanophosphate glasses

“…Such nitridation‐induced clustering of modifier cations around the pyrophosphate Q 1 (P) units detected in the Raman might generate percolation channels and presumably act as weak regions in the structure . Modification of modifier cation environment should be accompanied by vibrational changes in Raman spectra in the low‐frequency part of the spectrum (<400 cm −1 ), yet no distinguishable changes are observed.…”

“…The latter was done by setting the areas of all the intensity peaks in the range of interest equal to 1. The band assignment of the Raman spectra was based on previously reported data for germanophosphate and oxynitride phosphate glasses …”

Physical properties of reactive RF sputtered a-IZON thin films.

“…In this context, as general rule, amorphous oxynitrides have much higher charge carrier mobility than a-Si [10][11][12]. At the same time, amorphous oxynitrides presents homogeneous uniformity and high structural stability even though simple binary oxides tend to crystallize [13,14]. Moreover, the indium zinc oxynitride (IZON) is an excellent semiconductor for band gap engineering applications due to an easy tunable band gap [15,16].…”