Tuning the carrier concentration using Zintl chemistry in Mg3Sb2, and its implications for thermoelectric figure-of-merit.

Zintl compounds are potential candidates for efficient thermoelectric materials, because typically they are small band gap semiconductors. In addition, such compounds allow fine tuning of the carrier concentration by chemical doping for the optimization of thermoelectric performance. Herein, such tunability is demonstrated in Mg3Sb2-based Zintl compounds via Zn(2+) doping at the Mg(2+) site of the anionic framework (Mg2Sb2)(2-), in the series Mg3-xZnxSb2 (0 ≤ x ≤ 0.1). The materials have been successfully synthesized using the spark plasma sintering (SPS) technique. X-ray diffraction (XRD) analysis confirms a single solid solution phase of Mg3-xZnxSb2 (0 ≤ x ≤ 0.1). The thermoelectric properties are characterized by the Seebeck coefficient, electrical conductivity, and thermal conductivity measurements from 323 K to 773 K. Isoelectronic Zn substitution at the Mg site presents the controlled variation in the carrier concentration for optimizing the high power factor and reduced thermal conductivity. These results lead to a substantial increase in ZT of 0.37 at 773 K for a composition with x = 0.10 which is ∼42% higher than undoped Mg3Sb2. The electronic transport data for the Mg3-xZnxSb2 (0 ≤ x ≤ 0.1) compound are analyzed using a single parabolic band model predicting that Mg2.9Zn0.1Sb2 exhibits a near-optimal carrier concentration for high ZT. The electronic structure of transport properties of these disordered Mg3-xZnxSb2 (0 ≤ x ≤ 0.1) is also studied using density functional theory and the results obtained are in good agreement with experimental results. The low cost, lightness and non-toxicity of the constituent elements make these materials ideal for mid-temperature thermoelectric applications.

Panoscopically optimized thermoelectric performance of a half-Heusler/full-Heusler based in situ bulk composite Zr(0.7)Hf(0.3)Ni(1+x)Sn: an energy and time efficient way.

All scale hierarchical architecturing, matrix/inclusion band alignment and intra-matrix electronic structure engineering, the so called panoscopic approach for thermoelectric materials has been demonstrated to be an effective paradigm for optimizing high ZT. To achieve such hierarchically organized microstructures, composition engineering has been considered to be an efficient strategy. In this work, such a panoscopic concept has been extended to demonstrate for the first time in the case of half-Heusler based thermoelectric materials via a composition engineering route. A series of new off-stoichiometric n-type Zr0.7Hf0.3Ni1+xSn (0 ≤x≤ 0.10) HH compositions have been modified to derive HH(1 -x)/full-Heusler (FH)(x) composite with an all scale hierarchically modified microstructure with FH inclusions within the matrix to study the temperature dependent thermoelectric properties. The structural analysis employing XRD, FE-SEM and HR-TEM of these materials reveal a composite of HH and FH, with hierarchically organized microstructures. In such a submicron/nano-composite, the electronic properties are observed to be well optimized yielding a large power factor; α(2)σ (∼30.7 × 10(-4) W m(-1) K(-2) for Zr0.7Hf0.3Ni1.03Sn) and reduced thermal conductivity (∼2.4 W m(-1) K(-1) for Zr0.7Hf0.3Ni1.03Sn) yielding a high ZT∼ 0.96 at 773 K for composition Zr0.7Hf0.3Ni1.03Sn which is ∼250% larger than the normal HH Zr0.7Hf0.3NiSn (ZT∼ 0.27 at 773 K). The enhancement in ZT of these composites has been discussed in terms of primary electron filtering, electron injection and several phonon scattering mechanisms such as alloy scattering, point defect scattering, and grain boundary scattering. The Bergman and Fel model is used to calculate effective thermoelectric parameters of these composites for comparing the experimental results.

Factors regulating the metastatic potential of benign giant cell tumour of bone--study of an unusual case with short review of literature.

Benign giant cell tumour of bone with metastases to other bones and lungs is extremely rare. Benign metastasising giant cell tumour is distinctly separate from multicentric giant cell tumour, primary and secondary malignant giant cell tumour. Factors regulating the local recurrence and metastatic potential of this benign tumour depend on its aggressiveness which can be better assessed by clinical and radiological parameters rather than the histopathological appearance. A benign giant cell tumour of ischium with metastasis to vertebra and lung over an eleven year period is discussed. Extreme paucity of literature prompted to publish the article. A short review of factors determining the recurrence and metastatic spread of benign giant cell tumour of bone is highlighted.

Ewing's sarcoma of bone--a study of 71 cases by fine needle aspiration cytology.

Fine needle aspiration cytology (FNAC) plays immense diagnostic role in Ewing's sarcoma of bone. As clinically and sometimes radiologically Ewing's sarcoma mimics osteomyelitis of bone, FNAC is of great help to distinguish these 2 lesions and can avoid unnecessary incisional biopsies in most of the cases. At present limb salvage therapy is replaced by chemotherapy and radiotherapy. Moreover most of the patients present with gross soft tissue involvement where exact categorisation of malignant bone tumour is not possible by radiological means. FNAC is of great benefit to the clinicians and the patients as it provides a quick and accurate report and surgical interventions can be avoided in most of the cases. This paper highlights the cytological appearance of Ewing's sarcoma of bone in 71 cases. A conclusive diagnosis can be made with the help of special stains and cell block study. The diagnostic accuracy was 100% without any complication.

CT-guided needle aspiration cytology (FNAC) of 112 vertebral lesions.

Aspiration cytology under CT-guidance was utilised as a diagnostic device in 112 lesions of vertebrae from January, 1985 till August, 1992. The age of the patients ranged from 6 years to 82 years. The materials were spread on glass slides, air-dried and stained by May-Grunwald and Giemsa method. In few cases part of the aspirated material was utilised for special stain and cell block preparation. Analysis of results showed metastatic tumours in 61 cases, Tuberculous lesions in 24 cases, Plasmacytoma in 6 cases, Giant cell lesion in 6 cases, Eosinophilic Granuloma in 3 cases, Chordoma in 3 cases, Ewing's sarcoma in 2 cases, Hodgkin's disease in 2 cases, Chondrosarcoma in 1 case and no definite diagnosis was given in 4 cases. These 4 cases on exploration and biopsy proved to be osteoblastoma (2), haemangioma (1) and undifferentiated sarcoma in the other. The giant cell lesions on histopathology proved to be aneuryamal bone cysts in 4 cases while osteoclastoma in 2 cases. The diagnostic accuracy was 96.4%. No complication was encountered in the present study. Early diagnosis by needle aspiration cytology (NAC) prevented unnecessary surgical exploration in majority of the cases and treatment could be started at the earliest.

Septum and adrenocortical function.

Dorsal septum is an intermediary centre in between the hippocampus and hypothalamus and it has got inhibitory influence over the hypothalamo-pituitary-adrenal axis. Stimulation of the dorsal septum manifested with fall in adrenocortical output whereas its lesion has opposite response. Ventral septum is a facilitatory area regarding activation of the hypothalamo-pituitary-adrenal axis. It is a balancing centre lying in between the higher central nervous system structures and the hypothalamus. Stimulation and lesion of the ventral septum led to rise and fall in adrenal venous 17-OHCS output respectively. Adrenocortical response to stress of burn was not blocked or inhibited following lesion of the dorsal as well as ventall septum.