Paragraph 1: Temperature; driver for the change of symmetry There are 3 different phases that are observed and each of them are influenced by temperature. In addition‚ in each phase‚ the polymorph exhibits different crystal structures. At room temperature of 298K‚ it will be in phase 3 where it takes the structure of monoclinic-C2/m. When the temperature rises to 396K‚ it undergoes a transition into Phase 2 also known as the high-temperature monoclinic-A2/a phase. At Phase 2‚ the lattice parameters
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PIEZOELECTRICITY AND APPLICATIONS Piezoelectricity is the ability of some materials such as crystals and certain ceramics‚ to generate an electric potential in response to applied mechanical stress or heat. If the piezo crystals are not short-circuited‚ the applied charge induces a voltage across the material. The word Piezo is derived from the Greek “Piezein”‚ which means to squeeze or press. The piezo material exhibits both “Direct piezo electric effect” as well as ‘Converse piezo electric
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Bonding in solids: Ionic solids Ionic solid crystals (e.g. NaCl) are held together by the Coulomb attractive interaction between ions with opposite sign (ionic bonding) e2 b U = −αk + m r r (α = 1.7476 for Na +Cl − ) (m ~ 10) k = 1 / 4πε 0 Madelung constant Ionic cohesive energy: 11 U0 = min U (r ) = −αk 1 − m r0 mb r0 = αk 1 m −1 Bonding in solids: Ionic solids Properties of ionic solid crystals: • relatively stable and hard • poor electrical/heat
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compound of interest and its contaminants • Basic technique: 1. dissolve impure sample in an "appropriate" hot solvent Part A: Choosing a Solvent Part B: Purification of Phenacetin 2. cool solution slowly to induce crystal growth 3. filter resulting mixture to isolate crystals Reading: Mohrig‚ Hammond & Schatz Ch. 15 pgs 183-197 Ch. 10 pgs 104-113 Ch. 14 pgs 174-182 • Scale: 5-10 mg discovery based research - a new material prepared in a lab 1‚000 kg + commercial applications - sugar
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References: [12] Hopkin M.‚ Moses R.‚ Zimcik D.‚ Henderson D.‚ Ryall T.‚ Soangler R.‚ “Active vibration suppression systems applied to twin tail buffeting”‚ 1998‚ Proceedings of the SPIE—The International Society for Optical Engineering‚ Vol. 3044‚ 413-420. [19] Provder‚ Theodore‚ “Smart coatings”‚ 2007 edition‚ Published by American Chemical Society [20] Radio Education
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Piezoelectric crystals are one of many small scale energy sources. Whenever piezoelectric crystals are mechanically deformed or subject to vibration they generate a small voltage‚ commonly know as piezoelectricity. This form of renewable energy is not ideally suited to an industrial situation. The ability of certain crystals to generate Piezoelectricity in response to applied mechanical stress is reversible in that piezoelectric crystals‚ when subjected to an externally applied voltage‚ can change
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Wood frog-protects its organs by freezing solid. Ice wine-frozen grapes-the shrunken nature of the grapes is due to water loss-the less water in grapes‚ the fewer ice crystals there are to damage the delicate membranes of the fruit. Sugar is a natural antifreeze- this is probably why people developed diabetes during ice age (younger dryas) and people nowadays are more frequently diagnosed with diabetes from November to Freburary‚ when it is colder. Natural selection survival rule-LOSE THE FINGER
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Pre Lab 1a. Hydrated compound: ionic compound which contain water molecules inside their crystal lattice. The water is not chemically bonded to the crystal in any way and can be extracted by heating the compound. 1b. Anhydrous compound: a compound without water. 2a. The dot means that there are water molecules present in the crystal lattice in a specific ratio. 2b. For every mole of copper sulfate‚ there are five moles of water. 2c. The molar mass of copper (II) sulfate is 159.61 grams/mol
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Principles of X-ray Diffraction Diffraction effects are observed when electromagnetic radiation impinges on periodic structures with geometrical variations on the length scale of the wavelength of the radiation. The interatomic distances in crystals and molecules amount to 0.15–0.4 nm which correspond in the electromagnetic spectrum with the wavelength of x-rays having photon energies between 3 and 8 keV. Accordingly‚ phenomena like constructive and destructive interference should become observable
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CHAPTER 3: CRYSTAL STRUCTURES & PROPERTIES ISSUES TO ADDRESS... • How do atoms assemble into solid structures? (for now‚ focus on metals) • How does the density of a material depend on its structure? • When do material properties vary with the sample (i.e.‚ part) orientation? Chapter 3- 1 ENERGY AND PACKING • Non dense‚ random packing Energy typical neighbor bond length typical neighbor bond energy • Dense‚ regular packing r Energy typical neighbor bond length
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