New Solids in As-O-Mo, As(P)-O-Mo(W) and As(P)-O-Nb(W) Systems That Exhibit Nonlinear Optical Properties.

Nikolay Gerasimchuk,Meriem Goudjil,Lauri Kivijarvi,Soma Khanra,Bruce Noll,Miles Pearson,Yu Ping,Frank Röminger

doi:10.3390/molecules26051494

Abstract

Interactions between well-mixed fine powders of As2O3, P2O5, MoO3, WO3 and Nb2O5 at different stoichiometry in quartz ampoules under vacuum at ~1000 °C in the presence of metallic molybdenum (or niobium), over several weeks, led to shiny dichroic crystalline materials being formed in cooler parts of the reaction vessel. An addition of small quantities of metals-Mo or Nb-was made with the aim of partially reducing their highly oxidized Mo(VI), W(VI) or Nb(V) species to corresponding Mo(V), W(V) and Nb(IV) centers, in order to form mixed valence solids. Sublimed crystals of four new compounds were investigated using a variety of techniques, with prime emphasis on the X-ray analysis, followed by spectroscopy (diffusion reflectance, IR, Raman and EPR), second harmonic generation (SHG), thermal analysis under N2 and air atmosphere, and single crystals electrical conductivity studies. The results evidenced the formation of new complex solids of previously unknown compositions and structures. Three out of four compounds crystallized in non-centrosymmetric space groups and represent layered 2D polymeric puckered structures that being stacked on each other form 3D lattices. All new solids exhibit strong second-harmonic-generation (SHG effect; based on YAG 1064 nm tests with detection of 532 nm photons), and a rare photosalient effect when crystals physically move in the laser beam. Single crystals’ electrical conductivity of the four new synthesized compounds was measured, and the results showed their semiconductor behavior. Values of band gaps of these new solids were determined using diffusion reflectance spectroscopy in the visible region. Aspects of new solids’ practical usefulness are discussed.

Highlights

In the late ’60 and early ’70 new types of seemingly simple inorganic compounds, such as stoichiometric niobates and titanates, quickly emerged as ferroelectic, piezoelectric and light modulating materials [1–3]
The approach of thoroughly heating mixed powders of metal oxides and pnictogen oxides led to the successful obtaining of new solid-state phases in quartz ampoules
It was possible to prepare mixed metal, mixed valent solid phases using typical in solid-state chemistry high temperature procedures, the process needs to be better designed to increase yield of crystalline phases

Summary

Introduction

In the late ’60 and early ’70 new types of seemingly simple inorganic compounds, such as stoichiometric niobates and titanates, quickly emerged as ferroelectic, piezoelectric and light modulating materials [1–3] The latter property was found to be especially valuable for practical uses and now is widely used in mobile telephones and doubling laser frequency applications in military and industry [4–6]. The modulation of light is the key characteristic of non-linear optical materials (NLOMs) The origin of such interesting and useful property is crystallization of the above inorganic solids in acentric and polar space groups due to intrinsic distortions of the transition metal-oxygen MO6 environment. Resilience to photons flux and stability at high temperatures of these compounds and phases was the second most practically valuable property

Methods

Results

Conclusion