Strontium electronic properties

Additional work on dielectrics includes deposition of silica, PABS (lead aluminum boron silicates), PLZT (lead lanthanum zirconium titanate) and BST (barium strontium titanate) on Si-Ti-Pt wafers (Figure 2). The wafer specimens were patterned with metal electrodes and electronic properties were characterized. 

Alkaline-Earth Titanates. Some physical properties of representative alkaline-earth titanates ate Hsted in Table 15. The most important apphcations of these titanates are in the manufacture of electronic components (109). The most important member of the class is barium titanate, BaTi03, which owes its significance to its exceptionally high dielectric constant and its piezoelectric and ferroelectric properties. Further, because barium titanate easily forms solid solutions with strontium titanate, lead titanate, zirconium oxide, and tin oxide, the electrical properties can be modified within wide limits. Barium titanate may be made by, eg, cocalcination of barium carbonate and titanium dioxide at ca 1200°C. With the exception of Ba2Ti04, barium orthotitanate, titanates do not contain discrete TiO ions but ate mixed oxides. Ba2Ti04 has the P-K SO stmcture in which distorted tetrahedral TiO ions occur. 

Stronlianile, 385 Strontium atomic size, 379 chemistry, 382 electron configuration. 378 heal of vaporization, 305 hydroxide, K,p, 383 ionization energies, 379 occurrence, 385 properties, 381 Structural formula, 31 Structural isomers, 327 Styrene, 345 Sublimation, 176 Substance, 28 pure, 29, 65, 70... 

The metal-donor bonds are predominantly ionic and become more labile for calcium, strontium, and barium compared to beryllium and magnesium. The solubility and stability of the complexes decrease from calcium to barium. The 1 1 adducts of NHCs with BH3 or BF3 (28 and 29) are thermally stable and can be sublimed without decomposition. This is in sharp contrast to the properties of conventional carbenes, which rely on a pronounced metal-to-ligand back donation and are, thus, not suited to forming adducts with electron-poor fragments such as... 

For some applications, such as the cathode materials in solid oxide fuel cells (see Section 5.4.4), a material is needed that can conduct both ions and electrons. The strontium-doped perovskites LaMn03 (LSM), and LaCr03 (LSC) have both these properties. 

In many of its chemical properties, radium is like the elements magnesium, caldum, strontium and barium, and it is placed in group 2, as is consistent with its 6s26pcls2 electron configuraUon. Its sulfate (Ksp — 4.2 a 10-1 ) is even more insoluble in water than barium sulfate, with which it is conveniently coprecipitated, Like barium and other alkaline earth metals, it forms a soluble chloride (X p = 0,4) and bromide, which can also be obtained as dihydrates, Radium also resembles the other group 2 elements in forming an insoluble carbonate and a very slightly soluble lodate (Xsp = 8.8 x 1(T10). 

We turn now to a very important class of materials that have the formula /IBC3, with the C frequently oxygen. Strontium titanate is a familiar example and one we shall use for illustrative purposes. Titanium is in the D4 column of the Solid State Table, having four electrons beyond its argonlike core. Strontium has two electrons outside its kryptonlike core, so we may think of the six valence electrons as having been transferred to the three oxygen atoms to form a simple ionic system. As we shall see, however, the titanium d states form the lowest conduction band and are important in the bonding properties as well. 

The atomic number of beryllium is one less than that of boron, which follows it on the periodic table. Strontium, which is directly below beryllium in period 5 of the periodic table has 34 more protons and 34 more electrons than beryllium. However, the properties of beryllium resemble the much larger strontium more than those of similar-sized boron. 

Lanthanum strontium manganate, known also as LSM, is known for its magnetoresistance properties, and is also used in solid oxide fuel cells (SOFC). Sonochemistry was used for its preparation [121]. Electron magnetic resonance (EMR) spectra of nanosized sonochemically sintered powders of Lao.7Sro.3Mn03 (annealed, Tc = 340 K) were studied. 

Recently Bednorz and Muller (1) reported possible superconductivity at 30 K in the metallic-oxide La-Ba-Cu-0 system. Subsequent work by Tanaka and co-workers (2) showed that the high temperature superconductivity is due to the solid solution La BaxCuO. y which forms in the K2NiFA-type structure. Making solid solutions with strontium instead of barium, Cava et. al. (3). were able to show bulk superconductivity at 38 K in La2 xSrxCuOA y. While solid solutions of the type La2.xMxCuOA y (M = Sr, Ba) have been known for some time, (4-5) magnetic and electron transport properties of these compounds had not previously been measured at low temperatures (i.e. <120 K). ... 

The system 8a La Cu Q chosen by Bednorz and Muller (1) for their first investigation of superconductivity was connected to the existence of metallic properties of the oxide BaLa CusOis+s recently isolated in Caen (2). However the method used for the synthesis did not lead to the expected oxide but to a mixture of phases. Fortunately, one of these latter phases was found to be at the origin of superconductivity. In fact the concerned oxide is a M liF -type oxide, La2-xBaxCu04-y, isolated and studied for its electron transport properties several years before in Caen (3-4). It was then shown by several authors (5-9) that the strontium isostructural oxide La2-xSrxCu04-y (10-11) and the calcium compound (3-4) were also superconductors with Tc values ranging form 20K to 40K. 

Physical and Chemical Properties Strontium is a member of the alkaline earth elements, with atomic number 38 and atomic mass 87.62. It possesses four stable isotopes Sr (0.56%), Sr (9.86%), Sr (7.00%), and Sr (82.58%) (Emsley 1992). The pure metal strontium, while less reactive than the alkali metals, is a strong reducing agent and requires appropriate handling. Strontium reacts vigorously with water to form SrOH, liberating Hj in the process. In its chemical characteristics it resembles calcium and barium, and has properties intermediate between these two elements. The strontium atom easily loses two electrons in the 5 s level to form the divalent ion Sr " ". This ion occurs in many... 

The substitution of the alkaline earth for lanthanum in different amounts has great impact on the electron-conducting properties. This is principally because strontium (and calcium or barium) has a valence of 2+ whereas lanthanum exists in the 3-i- form. Thus, as strontium is substituted for lanthanum, there arises a need to equilibrate the charge of the cations and oxygen anions in the perovskite. 

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