Pseudopolymorphic Phase Engineering for Improved Thermoelectric Performance in Copper Sulfides.

Polymorphism (and its extended form - pseudopolymorphism) in solids is ubiquitous in mineralogy, crystallography, chemistry/biochemistry, materials science, and the pharmaceutical industries. Despite the difficulty of controlling (pseudo-)polymorphism, the realization of specific (pseudo-)polymorphic phases and associated boundary structures is an efficient route to enhance material performance for energy conversion and electromechanical applications. Here, this work applies the pseudopolymorphic phase (PP) concept to a thermoelectric copper sulfide, Cu2- x S (x ≤ 0.25), via CuBr2 doping. A peak ZT value of 1.25 is obtained at 773 K in Cu1.8 S + 3 wt% CuBr2 , which is 2.3 times higher than that of a pristine Cu1.8 S sample. Atomic-resolution scanning transmission electron microscopy confirms the transformation of pristine Cu1.8 S low digenite into PP-engineered high digenite, as well as the formation of (semi-)coherent interfaces between different PPs, which is expected to enhance phonon scattering. The results demonstrate that PP engineering is an effective approach for achieving improved thermoelectric performance in Cu-S compounds. It is also expected to be useful in other materials.

Highly Enhanced Thermoelectric and Mechanical Properties of Bi-Sb-Te Compounds by Carrier Modulation and Microstructure Adjustment.

Bi0.42Sb1.58Te3 + x wt % Cu1.8S (x = 0, 0.03, 0.05, and 0.1) bulk materials with enhanced thermoelectric and mechanical properties were fabricated by a solid-state reaction and spark plasma sintering. The thermoelectric properties, such as electrical transport properties and thermal conductivity, are highly dependent on the Cu1.8S content. The highest value of ZT obtained for Bi0.42Sb1.58Te3 with 0.05 wt % Cu1.8S is 1.23 at 373 K, and an optimistic average ZT of 1.2 is achieved at temperatures in the range of 323-448 K, which is 34% higher than that of the pristine sample. The highly enhanced ZT of the doped sample is attributed to the increased electrical conductivity and reduced lattice thermal conductivity caused by the effective element doping and the multiscale phonon scattering by quantities of point defects, twin boundaries, and nanopores. Further, the hardness obtained for this sample is 1.02 GPa, which is increased by 16% in comparison with that of the pristine sample. The conversion efficiency of the doped sample is also significantly higher than that of the pristine sample. Therefore, Cu1.8S is considered to be a promising dopant for enhancing the thermoelectric and mechanical properties of Bi-Sb-Te-based thermoelectric materials.

[Minimally invasive therapy for hallux valgus with deformity of little toe varus].

OBJECTIVE: To explore clinical effect of minimally corrective osteotomy for the treatment of hallux valgus with deformity of little toe varus through small incision. METHODS: From January 2013 to June 2016, 168 hallux valgus patients with deformity of little toe varus were treated by minimally corrective osteotomy through small incision. Among them, 7 males and 161 females were aged from 22 to 75 years old with an average of(59.3±3.5) years old. Preoperative clinical manifestation mainly focus on red and swollen of bunion, pain around with metatarsal bones, and diagnosed as hallux valgus with deformity of little toe varus through small incision. Operative time, postoperative complications, pre and post-operative IMA(angle between the first and the second metatarsal bones), HVA (hallux valgus angle), LDA(valgus angle of the fifth metatarsal bones), MPA(valgus angle of little toe), IM4-5 (angle between the forth and the fifth metatarsal bones) and PASA(fixed angle of proximal joint), postoperative AOFAS score were used to evaluate foot function. RESULTS: One hundred and sixty-eight patients were followed up for 6 to 48 months with an average of (28.6±3.2) months. All wounds were healed well without infection, sinus tract and other complications. Operative time ranged from 16 to 28 min with an average of (18.3±2.1) min. IMA, HVA, LDA, MPA and IM A 4-5 were (10.1±2.1)°, (32.6±4.2)°, (6.9±2.3)°, (18.5±5.2)°, (15.1±2.9)°preoperatively, improved to (8.3±2.2)°, (10.9±2.9)°, (2.7±0.4)°, (6.5±1.6)°, (8.9±1.8)° postoperatively, and had significant differences before and after operation. While there was no difference in PASA before (9.1±2.1)°and after operation(8.7±1.9)°. AOFAS score were improved from (31.6±3.9) before operation to(83.7±5.2) after operation, but no significant difference(P>0.05). According to AOFAS score, 147 patients obtained excellent results, 13 good, 6 moderate and 2 poor. CONCLUSIONS: Minimally corrective osteotomy for the treatment of hallux valgus with deformity of little toe varus through small incision could obtain satisfied clinical effect, and has advantages of small incision, no stitches, beautiful appearance, shorter operation time, and rapid recovery. It is worth popularization in clinical practise.