CHAPTER ONE

            1.0  INTRODUCTION

Tungsten (vi) oxide, also known as tungsten trioxide or tungsten analysis, W03 is a chemical compound containing oxygen and transition metal tungsten it is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten is treated with alkali to produce W03 further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal. Tungsten trioxide has a rich history dating back to its discovery during the 18th century. Peter woulfe was the first to recognize a new element in the naturally occurring mineral wolframite. Tungsten was originally known as wolfram, explaining the choice of “W” for its elemental symbol. Sweetish chemist Carl Wilhelm Scheele contributed to its discovery with his studies on the mineral scheelite.

In 1841, a chemist named Robert Oxland gave the first procedures for preparing tungsten trioxide and sodium tungstate. He was grated patent for his work soon after and is considered to be the founder of systematic tungsten chemistry. 

In 1781, Carl Wilhelm Scheele discovered that a new acid, tungsten acid could be made from scheelite (at the time named tungsten). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid. In 1783, Jose and FaustoElhuyar found an acid made from Wolframite that was identical to tungstic acid later that year, at the Royal Beryara, Spain, and the brothers succeeded in isolating tungsten by reduction of this acid with charcoal and they are credited with the discovery of the element.

In World War II, tungsten played a significant role in background political dealings. Portugal as the main European source of the element was put under pressure from both sides because of its deposits of Wolframite ore at parasqueira. Tungsten desirable properties such as resistance to high temperatures, its hardness and density and its strengthening of alloys made it an important raw material for the arms industry both as a constituent of weapons and requirement ad employed in production itself e.g. in tungsten carbide cutting tools for machining steel. The name tungsten (from the Swedish tungsten “heavy stone”) is used in English, French and many other languages as the name of the element, but not in the Nordic Countries.

Tungsten was the old sweetish names for the mineral scheelite “Wolfram” (or “Volfram”) is used in most European (Especially Germanic and Slavic) languages and is derived from the mineral Wolframite which is the origin of the chemical symbol W. The name “Wolf rahm” (“Wolf Soot” or “Wolf Cream”) the name given to tungsten by Johan Gottschalk Wallerius in 1747. This in turn, derives “LupiSpuma”, the name Georg Agricota used for the element in 1546, which translates into English as “Wolf’s Froth” and is a reference to the large amount to tin consumed by the mineral during its extraction.

Tungsten trioxide is used for many purposes in everyday life. It is frequently. Used in industry to manufacture tungstate for x-ray screen Phosphors for fireproofing fabrics and in gas sensors Due to its rich yellow color is also used as a pigment in ceramics and paints. In recent years, tungsten trioxide has been employed in the production of electro-chromic windows or smart windows. These windows are electrically switchable glass that changes high transmission properties with an applied voltage. This allows the user to tint their windows changing the amount of heat or light passing through.

2010 ASIT report a quantum yield of 19% in photo catalytic water spitting with a cesium enhanced tungsten oxide photo catalyst.

In 2013, highly photo catalyst active titanic tungsten (vi) oxide/noble metal (Au and pt) composites toward oxalic acid were obtained by the means of selective noble metal photo deposition on the desired oxides surface either on (TiO2 or WO3) the composite showed a modest hydrogen production performance.

In 2016, shape controlled tungsten trioxide semi-conductors were obtained by the means of hydrothermal synthesis form these semi-conductors composite systems were prepared with commercial T102. This composite system showed a higher photo catalysis activity than the commercial T102 (Evonit Aeroxide P25) toward phenol and methyl orange degradation.

            1.2 PROBLEM STATEMENT

Although the stable phase of pure WO3 at 17 330 ◦C is monoclinic with the P21/n space group, any change in temperature may induce structural distortions and thereby cussing a phase transfer. Indeed, tungsten trioxide has an orthorhombic lattice at 330 740 ◦C and a tetragonal structure above 740 ◦ C. in addition, it can be crystallized in a ReO3 cubic system without a central atom. It is obvious that the electronic structure of WO3 is affected by its crystal symmetry. In order to investigate this issue, a more comprehensive comparative study of tungsten trioxide in its Bravais lattices both within theory and experiment is needed

            1.3   AIM OF STUDY

The main aim of this work is to carry out a comprehensive theoretical comparative study on cubic and monoclinic lattice of WO3 using DFT as implemented in Quantum ESPRESSO 

            1.4   OBJECTIVES

1.                  To analyze the structural properties of cubic and monoclinic tungsten trioxide.

2.                  To Study the electronic properties (Density of State (DOS)) of both cubic and monoclinic tungsten trioxide.

3.                  To investigates its possible applications

            1.5 SCOPE AND LIMITATIONS

During the course of this study we shall analyze the structural properties and also study the electronic properties of cubic and monoclinic tungsten trioxide using density functional theory.

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