Strengthening of Alkali Halides by Divalent-Ion Additions

Single crystals of NaCl, NaBr, KCl, and KBr containing divalent additions of Ca²⁺, Sr²⁺, and Ba²⁺ were tested mechanically. In the solution-treated condition, the yield strength, σ _v , as determined from compression testing in a 〈100〉 direction is essentially dependent on the concentration of the dopant only and is independent of the species of either the dopant or of the host material. All crystals soften on aging, with the exception of the NaCl:Ca²⁺, NaBr:Ca²⁺, and NaBr:Sr²⁺ systems. In addition, correlation was good between σ _v , and the Knoop hardness number, H , obtained by indentation with the long axis of the indenter aligned in 〈100〉. The equation is of the form σ _v = C ( H–H ₀), where C ≅ 0.21 for all four halide families and H₀ is near the hardness value of the pure halides. Furthermore, H ₀≅5×10⁻³E₁₁₁, the Young's modulus in the 〈111〉 direction. Hence σ _v ≅0.21 H –10⁻³E₁₁₁.     

Ferrimagnetic Resonance Line Widths and Phase Distributions in Sintered Yttrium Iron Garnets

Iron-rich phases in yttrium iron garnet specimens are easily detected by microscopic examination. These phases form as pockets in the yttrium iron garnet matrix at low sintering temperatures but are swept into grain boundaries at higher temperatures. The dependence of ferrimagnetic resonance line width on composition and sintering conditions is given. Low line widths are realized when gas-generation problems are controlled. Line widths as low as 15 oersteds have been obtained.     

Arsenate Glasses

Stability regions were determined for a new family of glasses. Arsenic pentoxide (As₂O₅) forms binary glasses with alkali metal oxides (except Li₂O) and the known glass-formers B₂O₃, P₂O₅, GeO₂, and TeO₂. It also forms ternary glasses with Li₂O and a variety of alkaline earth, transition metal, and post-transition metal oxides when gallium oxide (and in some instances indium oxide) is present as a third component.     

New Arsenate Glasses

A variety of new ternary arsenate glasses formed from mixtures of ionic alkali-metal meta-arsenates (MAsO₃) with somewhat covalent higher valence metal oxides (MO_x) have been prepared. From rate-of-hydrolysis comparisons, it has been found that bonding in these glasses is enhanced by de-protonization. The latter is enhanced through processing using alkali-metal flourides and increases the number of direct oxygen links between the higher valence metals. Stabilization also tends to increase with the covalent bonding or chain-forming character of the latter metals as well as with the electrostatic binding between alkali-metal ions and the chain linkage oxygens.     

Melting-Point Relations for Simple Halides and Oxides

For simple halides and oxides, melting point ( T_f ) is related to structure, bond length ( d ), ionization, and exchange. For many structurally related series, the parameter T_f d ² increases linearly with ( ip·ea ) ⁻¹, where ip is the first ionization potential of the metal and ea is the electron affinity of the anion-forming atom. Deviations from this relation can be attributed to internal coupling, catenation exchange, and exchange between atoms that form anions.     

Growth of Large Optical-Quality Yttrium and Rare-Earth Aluminum Garnets

An improved flux consisting of PbO-PbF₂ and B₂O₃ was developed for the growth of garnets. Rare-earth aluminum garnet crystals weighing in excess of 100 g and modified yttrium aluminum garnet crystals weighing up to 60 g were obtained using this flux. Lead contamination was reduced to noncritical levels in these crystals by working with large excesses of A1₂O₃ in the melt. Excellent optical quality has been produced as indicated both by visual examination and by outstanding laser performance.     

Relations Between Normal Boiling Point and Melting Point for Simple Halides and Oxides

For most halides the normal boiling point ( T_b in kelvin units) is given by the relation: T_b= 440 n_c ( ip·ea·d ²) ⁻¹ , where n_c is the coordination number of the cation, ip the first ionization potential of the metal (in electron volts), ea the electron affinity of the anion former (in electron volts), and d the bond length in the crystal (in nanometers). Similar relations are found for oxides. For both classes the following relation applies: T_b/T_f= 1 + 0.67 /V _a , where TI is the melting point of the crystal and V_a is the valence of the anion. Exceptions occur when inert ( s² ) electron pairs form the outer shield of the cation or anion core, when electron spin pairing occurs between halogen or oxygen atoms, when there are direct interactions between metal atoms, or when n_c is not the same in the molten and crystalline states. Further, it is shown that covalency related to the asymmetric polarization of anions by cations with partially filled valence shells can markedly increase cohesion in the melt. This relates to plasticity in the solid as well.