Optical and Electrical Behavior of Gel Grown Strontium Incorporated Nickel Cadmium Oxalate Trihydrate Crystals for Opto-Electronic Applications

Crystal growth is the field of growing new variety of crystals for scientific and commercial purposes. Crystal growth in gels is an efficient and inexpensive technique to grow water insoluble single crystals at ambient temperature [1-4]. The chemically inert gel permits the reagents to diffuse at a desirable controlled rate. In recent years crystal growth in silica gel medium has attracted the attention of many researchers [5]. The growth of various mixed crystals like rare earth mixed crystals; transition metal mixed crystals has become an interesting field in the modern years, particularly after the discovery of ceramic superconductors [6]. Due to their extended and endless periodicity of atoms or molecules throughout the specimen, single crystalline solids are considered to be compelling class of materials [7]. For the elemental research in the field of organic electronics, the organic single crystals and organo-metallic compounds are considered to be influential materials because of the grain boundary vacancy, presence of minimum amount of impurities, unique structure, excessively good surface crystallinity and excellent interface quality [8]. Microelectronics and optoelectronics are regarded as the fields in which single crystals are stipulated and they are used as structural, high temperature materials [9]. The present paper aims to carry out the growth and characterization of strontium incorporated nickel cadmium oxalate (SNCO) single crystals in silica gel at ambient temperature. Generally, most of the oxalate crystals exhibit water insolubility, corrosion resistance, insulating behaviour, possesses high leakage resistance and good thermal stability [10]. In view of this, the grown crystals were subjected for various characterization techniques.

EXPERIMENTAL:

MATERIALS AND METHODS

The crystallization of SNCO was done using single diffusion gel technique. Chemicals used for growing SNCO crystals are Sodium Meta Silicate (Na₂SiO₃.5H₂O), Oxalic acid (C₂H₂O₄.2H₂O), Nickel chloride (NiCl₂.6H₂O), Cadmium chloride (CdCl₂.2.5H₂O) and Strontium chloride (SrCl₂.9H₂O) of AR grade. The silica gel was set by acidification of sodium metasilicate (SMS) by oxalic acid so that the pH of the solution was brought to the desired value.

General procedure:

After setting the gel, strontium chloride, nickel chloride and cadmium chloride solution was poured over the surface of the gel with the ratio (0.2ml : 2ml : 2ml) along the sides of the test tube in such a way that the gel should not be disturbed. The gel is a semisolid, and hence a semisolid-liquid interface was setup and Ni²⁺, Cd²⁺ and Sr²⁺ cations from the supernatant solutions are diffused into the gel in an accurately composed manner through the fine pores in the gel. Within three weeks crystal attain maximum size and no further growth is observed [11-12]. The experiment was repeated by modifying the growth parameters such as concentrations of supernatant solutions, pH, specific gravity and density of the gel medium. Between 1.030 and 1.060 g.cm^-3, the specific gravity of the gel was varied. 1.036 to 1.046 g.cm^-3 is considered to be the gel density at which the crystals of good quality with maximum size are obtained [13-14]. The gel density above 1.050 g.cm^-3, there is non-uniformity in the surface of the grown crystals. The values of pH of the gel are set at 4, 5, 6, 7 and 8. There is reduction in the size of the crystal as the pH increases above 5 and good quality crystals are obtained when the pH of the gel is below 5. The molarity of oxalic acid was varied from 0.1 M–0.7 M and for the supernatant solutions like nickel chloride, cadmium chloride and strontium chloride, the variation range is between 0.2 M-1 M to recognize changes in the crystallization [15-16]. At descended concentration of the reactants the crystal size was diminished and larger sized crystals are obtained at higher concentration of the reactants. The optimum conditions to obtain good quality and larger sized crystals are summarized in Table 1. The growth setup for SNCO crystals and fully-grown crystals are shown in Figure 1.

Table 1: Growth Profile of SNCO crystal.