Stabilization of Metastable Thermoelectric Crystalline Phases by Tuning the Glass Composition in the Cu-As-Te System.

Recrystallization of amorphous compounds can lead to the stabilization of metastable crystalline phases, which offers an interesting way to unveil novel binary or ternary compounds and control the transport properties of the obtained glass ceramics. Here, we report on a systematic study of the Cu-As-Te glassy system and show that under specific synthesis conditions using the spark-plasma-sintering technique, the α-As2Te3 and ß-As2Te3 binary phases and the previously unreported AsTe3 phase can be selectively crystallized within an amorphous matrix. The microstructures and transport properties of three different glass ceramics, each of them containing one of these phases with roughly the same crystalline fraction (∼30% in volume), were investigated in detail by means of X-ray diffraction, scanning electron microscopy, neutron thermodiffraction, Raman scattering (experimental and lattice-dynamics calculations), and transport-property measurements. The physical properties of the glass ceramics are compared with those of both the parent glasses and the pure crystalline phases that could be successfully synthesized. SEM images coupled with Raman spectroscopy evidence a "coast-to-island" or dendriticlike microstructure with microsized crystallites. The presence of the crystallized phase results in a significant decrease in the electrical resistivity while maintaining the thermal conductivity to low values. This study demonstrates that new compounds with interesting transport properties can be obtained by recrystallization, which in turn provides a tuning parameter for the transport properties of the parent glasses.

Polymorphism in Thermoelectric As2Te3.

Metastable ß-As2Te3 (R3̅m, a = 4.047 Å and c = 29.492 Å at 300 K) is isostructural to layered Bi2Te3 and is known for similarly displaying good thermoelectric properties around 400 K. Crystallizing glassy-As2Te3 leads to multiphase samples, while ß-As2Te3 could indeed be synthesized with good phase purity (97%) by melt quenching. As expected, ß-As2Te3 reconstructively transforms into stable α-As2Te3 (C2/m, a = 14.337 Å, b = 4.015 Å, c = 9.887 Å, and ß = 95.06°) at 480 K. This ß â†’ α transformation can be seen as the displacement of part of the As atoms from their As2Te3 layers into the van der Waals bonding interspace. Upon cooling, ß-As2Te3 displacively transforms in two steps below T(S1) = 205-210 K and T(S2) = 193-197 K into a new ß'-As2Te3 allotrope. These reversible and first-order phase transitions give rise to anomalies in the resistance and in the calorimetry measurements. The new monoclinic ß'-As2Te3 crystal structure (P2(1)/m, a = 6.982 Å, b = 16.187 Å, c = 10.232 Å, ß = 103.46° at 20 K) was solved from Rietveld refinements of X-ray and neutron powder patterns collected at low temperatures. These analyses showed that the distortion undergone by ß-As2Te3 is accompanied by a 4-fold modulation along its b axis. In agreement with our experimental results, electronic structure calculations indicate that all three structures are semiconducting with the α-phase being the most stable one and the ß'-phase being more stable than the ß-phase. These calculations also confirm the occurrence of a van der Waals interspace between covalently bonded As2Te3 layers in all three structures.

Assessing Environmental Control Strategies in Cage-Free Egg Production Systems: Effect on Spatial Occupancy and Natural Behaviors.

Animal welfare concerns have been a challenging issue for producers and international marketing. In laying hen production, cage-free systems (CFS) have been identified as an alternative to ensure the laying hens' well-being. Nevertheless, in CFS, important environmental issues have been reported, decreasing indoor air quality. Environmental control strategies (ECS) have been designed to enhance indoor air quality in CFSs. However, little information exists about the effect of these ECSs on natural animal behaviors. Four strategies and one control were tested in an experimental CFS, previously designed to track behavioral variables using video recordings over seven time-lapses of 1 hour per day. Spatial occupancy (SO) and laying hen behaviors (LHB) were registered. One statistical analysis was applied to evaluate the effect of ECS on SO and LHB using a multinomial response model. Results show lower chances to use litter area within the reduction of litter allowance treatment (T17) (p < 0.05). Neither the four ECSs nor the control implemented in this experiment affected the natural behaviors of the hens. However, stress patterns and high activity were reported in the T17 treatment. This study shows that it is possible to use these ECSs without disrupting laying hens' natural behaviors.