Phase equilibria in the Ag4SSe-SnTe system

The phase diagram of the system Ag₄SSe-SnTe is studied by means of X-ray diffraction, differential thermal and metallographic analyses and measurements of the microhardness and the density of the material. This diagram is divided into two eutectic-type subdiagrams by the composition Ag₄SSe·2SnTe. The unit-cell parameters of the intermediate phases 3Ag₄SSe·SnTe (phase A) and -Ag₄SSe·2SnTe (phase B) are determined as follows: for phase A: a=0.7851 nm, b=0.7196 nm, c=0.6296 nm, =101.32°, =85.90°, =111.36°; for phase B: a=0.3662 nm, b=0.3303 nm, c=0.3343 nm, =90.74°, =108.94°, =91.91°. The phase Ag4SSe·2SnTe melts congruently at 615°C and a polymorphic transition of the phase takes place at T _- =110°C.This revised version was published online in November 2005 with corrections to the Cover Date.     

Phase equilibria in the Ag4SSe–As2Se3 system

The phase diagram of the system Ag₄SSe–As₂Se₃ is studied by means of X-ray diffraction, differential thermal analyses and measurements of the microhardness and the density of the materials. The unit-cell parameters of the intermediate phases 3Ag₄SSe·As₂Se₃ (phase A) and Ag₄SSe·2As₂Se₃ (phase B) are determined as follows for phase A: a=4.495 Å, b=3.990 Å, c=4.042 Å, α=89.05°, β=108.98°, γ=92.93°; for phase B: a=4.463 Å, b=4.136 Å, c=3.752 Å, α=118.60°, β=104.46°, γ=83.14°. The phase 3Ag₄SSe·As₂Se₃ and Ag₄SSe·2As₂Se₃ have a polymorphic transition α?β consequently at 105 and 120°C. The phase A melts incongruently at 390°C and phase B congruently at the same temperature.     

Synthesis and thermal decomposition of bismuth peroxotitanate to Bi2Ti2O7

Bi-peroxotitanate was synthesized by a peroxo method and after thermal decomposition Bi₂Ti₂O₇ was obtained. DTA, TG and DSC curves of Bi₂[Ti₂(O₂)₄(OH)₆]5H₂O were recorded and used to determine isothermal conditions suitable for obtaining the intermediate samples corresponding to the phases observed during the thermal decomposition. The samples were identified by quantitative analysis, IR spectroscopy and X-ray analysis. The experimental results were used to propose a mechanism of thermal decomposition of the investigated compound to a nanosized Bi₂Ti₂O₇. The optimum conditions were also determined for obtaining Bi₂Ti₂O₇, which is applicable for piezosensors.     

Synthesis and thermal decomposition of neodymium(III) peroxotitanate to Nd<Subscript>2</Subscript>TiO<Subscript>5</Subscript>

Neodymium(III) peroxotitanate is used as a precursor for obtaining Nd₂TiO₅. The last one possesses numerous valuable electrophysical properties. TiCl₄, Nd(NO₃)₃·6H₂O and H₂O₂ in mol ratio 1:2:10 were used as starting materials. The reaction ambience was alkalized to pH = 9 with a solution of NH₃. The obtained neodymium(III) peroxotitanate and intermediate compounds of the isothermal heating were proved by the help of quantitative analysis and infrared spectroscopy (IRS). It has Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O composition. The absorption band observed in IRS at 831 cm^?1 relates to a triangular bonding of the peroxo group of Ti, at 1062 cm^?1—terminal groups Ti–OH and at 1491 and 1384 cm^?1—the bridging OH^?-groups Ti–O(H)–Ti. Nd₂TiO₅ was obtained by thermal decomposition of neodymium(III) peroxotitanate. The isothermal conditions for decomposition were determined on the base of differential thermal analysis, thermogravimetric and differential scanning calorimetry results in the temperature range of 20–1000 °C. The mechanism of thermal decomposition of Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O to Nd₂TiO₅ was studied. In the temperature range of 20–208 °C, a simultaneous decomposition of the peroxo groups by the separation of oxygen and hydrate water is conducted and Nd₄[Ti₂O₄(OH)₁₂] is obtained. From 208 to 390 °C, the terminal OH^?-groups are separated and Nd₄[Ti₂O₇(OH)₆] is formed. In the range of 390–824 °C, the bridging OH^?-groups are completely decomposed to Nd₂TiO₅. The optimal conditions for obtaining nanocrystalline Nd₂TiO₅ are 900 °C for 6 h and 20–80 nm.     

Rapana thomasiana hemocyanin (RtH): comparison of the two isoforms, RtH1 and RtH2, at 19A and 16A resolution

Three-dimensional (3D) reconstructions of the two 8.4 MDa Rapana thomasiana hemocyanin isoforms, RtH1 and RtH2, have been obtained by cryoelectron microscopy of molecules embedded in vitreous ice and single particle image processing. The final 3D structures of the RtH1 and RtH2 didecamers at 19 A and 16 A resolution, respectively, are very similar to earlier reconstructions of gastropodan hemocyanins, revealing structural features such as the obliquely oriented subunits, the five- and two-fold symmetrical axes. Three new interactions are defined; two of them connecting the arch and the wall while the third is formed between the collar and the wall. The collar-wall connection and one of the arch-wall connections are positioned between two individual subunit dimers, while the second arch-wall connection is located between two subunits within the subunit dimer. All three interactions establish connections to the first tier of the wall. Furthermore, for each interaction we have allocated two first tier functional units most likely involved in forming the connections.     

Phase equilibria in the CdI2-Ag2Se system

The phase diagram of the system CdI₂-Ag₂Se is studied by means of X-ray diffraction, differential thermal analysis and measurements of the density of the material. The unit cell parameters of the intermediate phase 2CdI₂·3Ag₂Se were determined a = 0.6387 Å, b = 4.311 Å, c = 4.044 Å; α = 113.72°, β = 90.27° and γ = 94.85°. The intermediate phase 2CdI₂·3Ag₂Se has a polymorphic transition at 125 °C. It melts incongruently at 660 °C.     

Thermal decomposition of cadmium peroxotitanate to CdTiO3

TG, DTA and DSC curves of Cd₂[Ti₂(O₂)₂O(OH)₆]·H₂O were recorded and used to determine the isothermal conditions suitable for obtaining the intermediate samples corresponding to the phases observed during the thermal decomposition. The samples were identified by quantitative analysis, IR spectroscopy and X-ray analysis. The experimental results were used to propose a mechanism of thermal decomposition of the investigated compound to CdTiO₃. The optimum conditions were also determined for obtaining CdTiO₃ with well-defined crystallinity.     

Synthesis and thermal decomposition of potassium peroxotitanate to K2Ti2O5

Potassium peroxotitanate was synthesized by the peroxo method. During the thermal decomposition K₂Ti₂O₅ can be obtained. The isothermal conditions for decomposition of K₂[Ti₂(O₂)₂(OH)₆]·3H₂O were determined on the base of DTA, TG and DSC results. DTA and TG curves were recorded in the temperature range 20 and 900°C at a heating rate of 10°C min^–1. The obtained intermediate compounds were characterized by means of quantitative analysis and IR spectroscopy. The mechanism of thermal decomposition of K₂[Ti₂(O₂)₂(OH)₆]·3H₂O to K₂Ti₂O₅ was studied. The optimal conditions for obtaining K₂Ti₂O₅ were determined (770°C for 10 h).