Final writing exercise Essay Example for Free

Final writing exercise EssayThere are tierce descriptors whereby each has a different watch glass structure at three different temperatures. At room temperature (298K), Phase III is present whereby Cs3H(SeO4)2 has a watch crystallization structure of a monoclinic with a space group of C2/m. At 400K, Phase II is present whereby Cs3H(SeO4)2 has a crystal structure of a monoclinic-A2/a harmony. At 470K, Phase I is present whereby Cs3H(SeO4)2 has a crystal structure of a trigonal with a space group of R3-m. In Phase III, as we can see in Figure 2(a), the stance of the tetrahedrons is parallel to the a-axis, and in between these SeO4 tetrahedrons are the hydrogen sticks. Looking at a 2dimensional perspective, we can in any case see that in that respect is a translation bunkment of the SeO4 tetrahedrons along the a-axis hence the symmetry operator would be a glide line parallel to a-axis. In a 3-dimensional perspective, we can see that Phase III has a 2-fold rotation axis a nd contains glide planes.In Phase II, from Figure 2(b), we can see that the positioning of the SeO4 tetrahedrons are along the approximate direction 310. Observing the schematic of the crystal structure in Phase II, we can see that there is a good mirror line in between the SeO4 tetrahedrons. There is also an a-glide reflection vertically. In Phase I, from Figure 2(c), the positioning of SeO4 tetrahedron is similar to that of Phase II, however the expiration is the crystal structure and the hydrogen bonding. Comparing both Phase II and Phase III crystal structures of the compound, Phase II contains two-fold screw axis, inversion pith and a two-fold rotation axis, which is the sole reason for Phase II to be twice of that of Phase III in terms of geometricalarrangement of hydrogen bonds.From the above analysis of the symmetry of the crystals structures in different stagecoachs, we can tell that Phase III has the most symmetry operators and hence achieving the highest crystal symme try generating a low geometrical arrangement of hydrogen bonds. Due to the low geometrical arrangement of hydrogen bonds, the mobility of protons decreases giving the result of ferroelasticiy. The drastic change from superprotonic conductivity to ferroelasticty happens when there is a change from Phase II to Phase III. The major difference between theses 2 phases is the hydrogen bond arrangement.Paragraph 2Under the optic microscope, we can observe that the polymorphic domains will alter at each phase transition to a different extent. We can see in phase III that the domains in the Cs3H(SeO4)2 crystal are made up of polydomains separated by two kinds of domain boundaries. The two kinds of domain boundaries are categorized as the planes of 311 and 11n, where n is determined by the strain compatibility condition. The domains at the sides of each domain boundary are related to the reflective symmetry or the rotational symmetry on that boundary itself. Furthermore, we can observe that the angle between any domain and its neighboring domains is approximately long hundred, which is very close to the theoretical determine calculated using the lattice parameters.As we move on from phase III to phase II, we can observe that the domain structure alters slightly by the phase transition of TIIIII. Similarly, the reflective symmetry and rotational symmetry also changes at the aforementioned(prenominal) phase transition. However, the kinds of domain and domain boundary remain the same as those in phase III despite a change in domain pattern. This could be due to the slight change in confederation of hydrogen bonding between the SeO4 tetrahedrons when the existing hydrogen bonds were broken to form new weakerones. This might explains why their lattice parameters a and b do not really change appreciably. Compared to phase III previously, the angle between any domain and its neighboring domains in phase II is also approximately 120 and is justified by the theoretical value s determined from the same equation we used for phase III.Hence, this suggest a slight change in the Cs3H(SeO4)2 crystal structure at the phase transition of TIIIII. From phase II to phase I, the domain boundaries is observed to have disappear just before the curie temperature of the phase transition of TIII and the crystal structure changes fromoptically biaxial to optically uniaxial. This could be due to an external stress caused by the atomic rearrangement of the SeO4 tetrahedrons in the Cs3H(SeO4)2 crystal as a result of come offing the hydrogen bonds between them.Paragraph 3Higher temperatures for most material will enable atoms to move to low energy sites, fitting into a perfect crystal symmetry. Cs3H(SeO4)2 however behaves differently. As the temperature increases (above 396K), its crystal symmetry decreases when it changes phase from III to II. The orientation of the hydrogen bond for phase II and III differs. For phase II, the orientation is along 310 and 3-10 direction wh ereas for phase III, it is parallel to the aaxis. As the transition from phase III to II occurs, the harbinger of the superprotonic conductivity is observed. In order for vogue of proton to occur, the breaking and then recombination of hydrogen bonds are required.For phase III, in order for the movement of one proton, the breaking of 2 hydrogen bonds is needed. The reason as to why 2 hydrogen bond is needed to be broken and recombined again is because for the movement of one proton to occur, it must break the hydrogen bond it resides in and then change its orientation, recombining at an otherwise site the mirroring effect of opposite hydrogen bond is required to maintain the crystal symmetry i.e. to say that the another hydrogen bond parallel to the previous hydrogen bond site needs to be broken and recombined at other site parallel to the newlyrecombined hydrogen bond.In this way, in phase III, the recombination of two hydrogen bonds is simultaneously needed for one proton transpo rt. Phase II however, behaves differently. The movement of the proton is independent of the other protons at other hydrogen site. The crystal structure vacates for this flexibility of the proton motion, which the superprotonic conduction takes place. The mechanism in which proton transportation occurs in the polymorphs is by the diffusion of protons through a hydrogen bond network, by the cleaving and formation of the hydrogen bonds. However, in certain phases, the cleavage and formation of the hydrogen bond might differ. The supply cell works on the basis of the movement of protons. The movement of electrons should be disallowed as it would short circuit the fuel cell. Hence, a membrane is used to allow only the movement of protons across and not electrons and gases. On top of that, in order for a superprotonic effect to occur, the flexibility for proton motion must be allowed. Hence, the lesser symmetrically patterned the phases the protons reside in, the higher this flexibilit y.