Hello, everyone. In this lecture, we are going to talk about the definition of metals and ceramics. As you know, materials can be divided into two categories. One is inorganic materials, including metals and ceramics. The other one is organic materials. It is polymer. But firstly, metals, one of the inorganic materials, consist of atoms held together by delocalized electrons. So they should overcome the repulsion between ion cores. From this periodic table, you can find a lot of metals in many main group, transition and inner transition element. Metals include alloys, the combination of metallic element, and also include the intermetallic compound, the combination of metallic and nonmetallic elements. For example, the bismuth telluride is an intermetallic compound with two metallic bismuth and three nonmetallic tellurides with charging neutrality. The characteristic properties of metals can be determined by delocalized electrons. Thus, they show high electrical conductivity and also have high thermal conductivity due to the rapid contribution by electronic and polar transport. The metals have close packed structure, so they can be deformed plastically even at room temperature. Metals have non-directional metallic bonding and electron cloud that shield the cores. Bonding energy of a metal is relatively lower. So we can find the small nearest neighbor distance in close packed structure, such as a simple cubic, body-centered cubic, face-centered cubic, and hexagonal close packed structure. The first close packed structure is simple cubic structure. In this scheme, you can find eight, one over eight atoms at the corner of a unit cell. So the collision number of SCC a sixth. Atomic packing factor is defined by volume of atoms in unit cell over volume of a unit cell. We need one assumption that all atoms are hard spheres. The atomic packing factor for SCC is given by, the number of atoms in the unit cell, 1 times 4 over 3pi, 0.5a to the 3 over a to the 3. It makes 0.52. Due to this low packing factor, the simple cubic structure is rarely found in real materials. The second closed packing structure is BCC, the body-centered cubic structure. In this scheme, you can find one atom at the center of unit cell and also find eight 1 over 8 atoms at the corner of a unicell. So the coordination number of a BCC is 8. Atomic packing factor for a BCC is given by the number of atoms in the unit cell, 2 times 4 over 3pi, 3 to the 1 over 2, a over 4 to the 3, over a to the 3. It makes 0.68. Due to this higher packing factor, a lot of metals such as chrome, tungsten, alpa ion, tantalum, molybdenum have this BCC structure. Third, close packing structure is FCC, the face-centered cubic structure. In this scheme, you can find six 1 over 2 atoms at each phase, and also find eight 1 over 8 atoms at the corner of unit cell. So the coordination number of FCC is 12. Atomic packing factor for FCC is given by the number of atoms in the units are four, times 4 over 3pi, 2 to the 1 over 2, a over 4 to the 3, over a to the 3. It makes 0.74. So this high packing factor originated from the stacking sequence, ABCABC. So a lot of metal elements, aluminum, copper, gold, lead, nickel, platinum, silver have this FCC structure. The high packing factor of 0.74 is also found in HCP, hexagonal close packing structure. The condition number of HCP is also 12. Just the difference between the FCC structure is the stacking sequence as shown here, you can find the ABAB stacking sequence. So a lot of metals such as cadmium, magnesium, titanium, zinc have this HCP structure. On the other hand, ceramics consist of arrays of interconnected atoms. So nonmetallic inorganic solids and all inorganic semiconductors are ceramics. The names of ceramics are determined by the anion. So the oxide are the combination of a metallic cationic and anionic oxidant. Nitrite are the combination of metallic cation and anionic nitrogen. So carbides, the boride, silicide, sulfide are ceramics. Ceramics also include glass. Ceramics have mixed bonding or combination of covalent, ionic, and sometimes metallic bonding. This ceramic bonding is related with the electronegativity. For example, the calcium chloride has large difference in electronegativity between two elements. So the bonding characteristic of this material is strong ionic, while the silicon carbide has very small difference in electronegativity. So silicon carbide has strong covalent bonding characteristics. The crystal structure of ceramics can be understood by oxide structure, because ionic radius of oxygen anion is radial than that of metallic cation. So we can start from the close packed structure of oxygen ions in a lattice such as face-centered cubic, and then cation can be incorporated into the host. So side relationship cation to anion, and charge in neutrality. These two parameters are very important for crystal structures of ceramics. Then crystallographic arrangement and stoichiometry of ceramics can be determined by these two parameters. The ceramics should have charge neutrality. Charge neutrality means that net charge equal zero. So the ceramics with composition Ma+xAb-y, that suggest that a times x plus minus b times y should be zero. So we can find so many ceramic composition such as NaCl, ZnO, Al2O3, SiO2, Nb2O5, WO3, based on the charge neutrality. Relative sizes of ions, actually, the size of cation to size of anion is linked with the structural stability of ceramics. Coalition number increased with the ionic radius of cation over ionic radius of anion. As shown here, the zinc sulfide, sodium chloride, cesium chloride is the combination of one metallic cation and one anion. But as shown here, you can find totally different crystal structure in these compound due to the difference in r cation over r anion. If this value is arranged from 0.225-0.414, the coordination numbers should be four. We can find a tetrahedral structure in zinc sulfide. If this value is ranged from 0.414 to 0.732, the coordination number should be 6. So we can find this octahedral cations to feature in sodium chloride. If this value is arranged from 0.732 to unity, the coordination number of this material should be 8. So we can find a cubic structure in cesium chloride. So you can obtain the numerical information about the ionic radius through this URL, which was provided by Shannon. You can find periodic table for database of ionic radii, and by just clicking on element, you can find details for a particular element, and obtained radii for a particular element according to charging and coordination number. So in this lecture, we briefly review the definition of the metals and ceramics, the position and their composition and crystal structure because the these two factors are important factor to determining the physical and chemical properties of inorganic materials. So in the next, we are talking about classification of ceramics. Thank you.
