The Association Between Antihypertensive Drug Use and Hospitalization for Pneumonia in the General Population: A Case-Crossover Study Using the National Health Insurance Database of Korea.

BACKGROUND: Previous studies have reported an association between pneumonia risk and the use of certain drugs. We investigated the relationship between antihypertensive drugs and pneumonia in the general population. METHODS: This case-crossover study utilized the nationwide data of South Korea. We included participants who were hospitalized for pneumonia. A single case period was defined as 30 days before pneumonia onset, and two control periods were established (90-120 and 150-180 days before pneumonia onset). Further, we performed sensitivity and subgroup analyses (according to the presence of diabetes, documented disability, and whether participants were aged ≥ 70 years). We used conditional logistic regression models adjusted for covariates, such as angiotensin-converting-enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), other antihypertensives, statins, antipsychotics, benzodiazepine, and the number of outpatient visits. RESULTS: In total, 15,463 subjects were included in this study. ACE inhibitors (adjusted odds ratio [aOR], 0.660; 95% confidence interval [CI], 0.558-0.781), ARBs (aOR, 0.702; 95% CI, 0.640-0.770), and other antihypertensive drugs (aOR, 0.737; 95% CI, 0.665-0.816) were significantly associated with reduced pneumonia risk. Subgroup analyses according to the presence of diabetes mellitus, documented disability, and whether participants were aged ≥ 70 years consistently showed the association of antihypertensives with a reduced risk of hospitalization for pneumonia. CONCLUSION: All antihypertensive drug types were related to a lower risk of hospitalization for pneumonia in the general population. Our results implied that frequent medical service usage and protective immunity were primarily related to a reduced risk of pneumonia in the general population of South Korea.

Association Between Antihypertensive Use and Hospitalized Pneumonia in Patients With Stroke: A Korean Nationwide Population-Based Cohort Study.

BACKGROUND: We aimed to examine the association between antihypertensive use and the incidence of hospitalized pneumonia in patients with a history of stroke. METHODS: In this case-crossover study, we obtained data from the Korean National Health Insurance Service-National Sample Cohort database. We included the data of patients with history of stroke who were admitted with a disease code of pneumonia. We analyzed the patients' exposure to antihypertensives in the 30 (single case period), 90-120, and 150-180 days (2 control periods) before the onset of pneumonia using conditional logistic regression analysis. Additionally, sensitivity analysis and subgroup analysis according to diabetes status, age, and documented disability were performed. RESULTS: Angiotensin II receptor blocker (ARB) use was associated with a reduced risk of hospitalized pneumonia (adjusted odds ratio [OR] [95% confidence interval; 95% CI]: 0.718 [0.576-0.894]). However, the use of angiotensin converting enzyme inhibitors and other antihypertensives were not associated with a change in hospitalized pneumonia incidence (adjusted OR [95% CI]: 0.902, [0.603-1.350] and 0.788 [0609-1.018], respectively). Subgroup analysis revealed that ARB use was associated with a reduced incidence of hospitalized pneumonia in patients with a history of stroke who were older than 65 years, but not in younger (≤ 65 years) group (adjusted OR [95% CI]: 0.687 [0.536-0.880]). CONCLUSION: ARB use is associated with a reduced incidence of hospitalized pneumonia in patients with a history of stroke, especially in older adults.

Spasticity and preservation of skeletal muscle mass in people with spinal cord injury.

STUDY DESIGN: Cross-sectional OBJECTIVE: To investigate the association between skeletal muscle mass and spasticity in people with spinal cord injury (SCI). SETTING: Tertiary level hospital in Seoul, Korea METHODS: Spasticity was evaluated in 69 participants with SCI using the spasticity sum score (SSS), Penn Spasm Frequency Scale (PSFS), and Spinal Cord Assessment Tool for Spastic Reflexes (SCATS). Skeletal muscle mass was measured using a dual-energy X-ray absorptiometry scanner, and skeletal muscle index was calculated by dividing skeletal muscle mass by height squared. Laboratory parameters including hemoglobin, albumin, creatinine, fasting glucose, and cholesterol were measured. Spearman's correlation analysis was performed to assess the association between the skeletal muscle mass and spasticity scales. Multiple linear regression analysis was used to present the independent association between them. RESULTS: The participants' mean age was 41.8 years; 54 (78.3%) were male, and 46 (66.7%) were tetraplegic. Skeletal muscle index of lower extremities was significantly correlated with all spasticity scales. Spearman's correlation coefficients were 0.468, 0.467, 0.555, 0.506, and 0.474 for SSS, PSFS, SCATS clonus, SCATS flexor, and SCATS extensor with p-values < 0.001, respectively. After adjustment for age, sex, level of injury, body mass index, and serum creatinine, all spasticity scales were significantly associated with skeletal muscle index of lower extremities in multiple regression analysis. Standardized coefficients were 0.228, 0.274, 0.294, 0.210, and 0.227 for SSS, PSFS, SCATS clonus, SCATS flexor, and SCATS extensor. CONCLUSIONS: Spasticity was significantly correlated with the skeletal muscle mass even after adjusting for possible confounders. Spasticity may need to be considered as an influencing factor in interventions such as electrical stimulation to preserve skeletal muscle mass.

Obesity cutoff values in Korean men with motor complete spinal cord injury: body mass index and waist circumference.

STUDY DESIGN: Cross-sectional. OBJECTIVES: To determine the obesity cutoff values for body mass index (BMI) and waist circumference (WC) in Korean men with motor complete spinal cord injury (SCI). SETTING: Tertiary level hospital in Seoul, Korea. METHODS: BMI (kg/m2) was calculated and WC (cm) was measured in each participant in the supine position. Percentage of total body fat (%) was determined using whole-body dual-energy X-ray absorptiometry. Receiver operating characteristic curves were generated to determine the obesity cutoff values for BMI and WC. The optimal cutoff values were determined using the Youden index. Identified cutoff values were compared with those of 195 age- and BMI-matched men in the general population (GP), obtained from the Korea National Health and Nutrition Examination Survey. RESULTS: This study included 52 Korean men with motor complete SCI. A BMI of 20.2 kg/m2 and WC of 81.3 cm were identified as obesity cutoff values in Korean men with motor complete SCI. The area under the curve (AUC) was 0.928, specificity was 100%, and sensitivity was 84.8% according to the ROC curve of BMI for participants. AUC was 0.964, specificity was 100%, and sensitivity was 84.8% in the ROC curve of WC for participants. A BMI of 22.5 kg/m2 and WC of 85.5 cm were identified as obesity cutoff values in age- and BMI-matched men in the GP. CONCLUSIONS: The obesity cutoff values in Korean men with motor complete SCI that were determined in this study were lower than those of the Korean GP and western people with SCI.

Traumatic peripheral nerve injuries in young Korean soldiers: a recent 10-year retrospective study.

PURPOSE: Traumatic peripheral nerve injury (PNI), which occurs in up to 3% of trauma patients, is a devastating condition that often leads to permanent disability. However, knowledge of traumatic PNI is limited. We describe epidemiology and clinical characteristics of traumatic PNI in Korea and identify the predictors of traumatic complete PNI. METHODS: A list of enlisted soldier patients who were discharged from military service due to PNI over a 10-year period (2012-2021) was obtained, and their medical records were reviewed. Patients were classified according to the causative events (traumatic vs. nontraumatic) and injury severity (complete vs. incomplete). Of traumatic PNIs, we compared the clinical variables between the incomplete and complete PNI groups and identified predictors of complete PNI. RESULTS: Of the 119 young male patients who were discharged from military service due to PNI, 85 (71.4%) were injured by a traumatic event; among them, 22 (25.9%) were assessed as having a complete injury. The most common PNI mechanism (n=49, 57.6%), was adjacent fractures or dislocations. Several injury-related characteristics were significantly associated with complete PNI: laceration or gunshot wound, PNI involving the median nerve, PNI involving multiple individual nerves (multiple PNI), and concomitant muscular or vascular injuries. After adjusting for other possible predictors, multiple PNI was identified as a significant predictor of a complete PNI (odds ratio, 3.583; P=0.017). CONCLUSIONS: In this study, we analyzed the characteristics of enlisted Korean soldiers discharged due to traumatic PNI and found that the most common injury mechanism was adjacent fracture or dislocation (57.6%). Patients with multiple PNI had a significantly increased risk of complete injury. The results of this study contribute to a better understanding of traumatic PNI, which directly leads to a decline in functioning in patients with trauma.

Multiple magnetic transition and magnetocaloric properties in the mixed valence Eu8CuNi2.5Si42.5 type I clathrate compound.

We investigated the magnetocaloric and electrical transport properties of the Eu8CuNi2.5Si42.5 clathrate compound, synthesized by an arc melting and annealing method. X-ray photoemission spectroscopy revealed a mixed valence state of Eu2+ and Eu3+. The low-field and low-temperature magnetic measurements indicated a multiple magnetic transition, from ferromagnetic near 35 K to antiferromagnetic at 25 K. Increasing the magnetic field led to the broadening of antiferromagnetic peaks and a final ferromagnetic state under high magnetic fields, indicative of spin reorientation. The transition from a ferromagnetic to an antiferromagnetic state was further corroborated by specific heat measurements. We noted spontaneous magnetization at low temperatures via magnetic hysteresis and Arrott plot analysis. The coexistence of an antiferromagnetic ground state (attributed to the Eu2+ ions) and ferromagnetic clusters (associated with the Ni2+ ions) was supported by spontaneous magnetization at low temperatures in the antiferromagnetic state. The magnetocaloric analyses revealed a high spin entropy change over a broad temperature range for Eu8CuNi2.5Si42.5, which implies its potential as a robust low-temperature magnetocaloric material, distinguished by its high refrigerant capacity.

Characteristics of Hirayama Disease in Young South Korean Soldiers.

BACKGROUND AND PURPOSE: The purpose of this study was to describe the clinical presentation and features in electrodiagnostic and imaging investigations of young South Korean males diagnosed with Hirayama disease (HD). METHODS: We reviewed the electronic medical records of South Korean enlisted soldiers who were diagnosed with HD and discharged from military service during 2011-2021. We investigated the clinical characteristics and results of electrodiagnostic and magnetic resonance imaging (MRI) investigations. We analyzed laterality and identified the involved muscles using needle electromyography (EMG). Loss of lordosis, localized cervical cord atrophy, loss of attachment between the posterior dura and subjacent lamina, asymmetric flattening of the cord, crescent-shaped mass in the posterior epidural space, and noncompressive intramedullary T2-weighted high signal intensity were investigated using neutral- or flexion-position MRI. RESULTS: Forty-two male patients aged 20.2±0.8 years (mean±standard deviation) were identified. All patients complained of hand weakness, and 10 complained of hand tremor (23.8%). Four patients (9.5%) had symptoms in both upper limbs, and five (11.9%) had sensory disturbances. Needle EMG revealed that muscles in the C7-T1 myotome were commonly involved, and C5-C6 involvement of the deltoid (10.5%) and biceps brachii (12.5%) was also observed. In cervical MRI, localized cord atrophy (90.0%) was the most characteristic finding, and cord atrophy was most severe at the C5-C6 level (58.3%). CONCLUSIONS: This is the first description of a large number of patients with HD in South Korea. The clinical presentation and features found in electrodiagnostic and imaging investigations will improve the understanding of HD in the young South Korean male population.

Hierarchical Phonon Scattering from Nano to Macro Scale in Ag-Nano/TiO2-Micro Particle-Decorated p-type Bismuth Telluride Bulk Composites.

We study the thermoelectric properties of a p-type Bi0.4Sb1.6Te3.4 (BST) composite with Ag nanoparticle-decorated TiO2 microparticles (US-Ag/TiO2). The dispersion of US-Ag/TiO2 particles, synthesized by an ultrasonication (US) method, into the matrix effectively decreases lattice and bipolar thermal conductivity, attributed to the scattering centers formed at nano and micro scales. The electron backscattering diffraction (EBSD) measurements revealed smaller grain sizes within the BST composite when paired with the US-Ag/TiO2 particle dispersion. These reduced grain sizes, alongside nanoparticle-decorated microparticles dispersed throughout the matrix, scatter phonons effectively from long- to short-wavelength phonons and subsequently decrease lattice thermal conductivity. While the power factors of the composites are reduced, significant suppression of lattice and bipolar thermal conductivity has led to an increase in the maximum zT value (1.4 at 325 K) for a 0.9 wt % US-Ag/TiO2 particle dispersion within the BST matrix. This particle dispersion in the BST composite consistently demonstrates a high zT value across an extensive temperature spectrum, leading to an exceptionally high average zTavg value (1.38 up to 400 K), which is superior to the other values from reported BST composites. Thus, this research indicates that the dispersion of nanoparticle-decorated microparticles within a thermoelectric material matrix can significantly improve thermoelectric performance, which has promising implications for practical applications in thermoelectric cooling and sustainable and economical energy harvesting technologies.

Prevalence of Neuromuscular Diseases in Young South Korean Males; A Korean Military Manpower Administration and Medical Command Data-Based Study.

BACKGROUND AND PURPOSE: All young males in South Korea must undergo a physical examination for their participation in military service. We aimed to determine the prevalence rate (PR) of various neuromuscular diseases in young South Korean males using the data of exempted patients and soldiers. METHODS: The number of males exempted based on specific items of physical examination corresponding to neuromuscular disease during 2011-2020 were obtained from the records of the Military Manpower Administration. The list of enlisted soldier patients who were discharged from military service due to neuromuscular diseases during 2011-2020 was obtained from the Armed Forces Medical Command, and their medical records were reviewed. RESULTS: The PR of neuromuscular diseases was calculated among 948 identified males: 713 exempted males and 235 soldiers. The PRs of overall hereditary neuropathies, Hirayama disease (HD), myasthenia gravis (MG), and inherited muscle diseases in South Korean males in their early 20s were 8.34 (95% confidence interval [CI], 7.39-9.30), 5.54 (95% CI, 4.76-6.32), 2.97 (95% CI, 2.40-3.55), and 10.38 (95% CI, 9.31-11.46) per 100,000 persons, respectively. Among the enlisted soldiers, hereditary neuropathy with liability to pressure palsy was the most common neuromuscular disease, with a prevalence among the enlisted soldiers of 3.11 (95% CI, 2.42-3.80) per 100,000 persons. Myotonic dystrophy was the most prevalent myopathy, followed by facioscapulohumeral muscular dystrophy. CONCLUSIONS: The 10-year PRs of hereditary polyneuropathies, HD, MG, and inherited muscle diseases in young South Korean males have been reported. These data could be valuable to understanding each neuromuscular disease in the young male population of South Korea.

Rehabilitation outcome in people with spinal cord injuries resulting from diving in South Korea.

STUDY DESIGN: Retrospective electronic medical record review combined with a telephone interview. OBJECTIVES: The purpose of this study was to describe the neurological and socio-professional outcomes of patients with diving injuries of the cervical spine. SETTING: A tertiary hospital and its affiliated rehabilitation hospital in South Korea. METHODS: Electronic medical records were reviewed for medical and neurological information. Telephone interviews were then conducted with questionnaire regarding specific circumstances at the time of injury and social status. RESULTS: A total of 33 patients with spinal cord injury (SCI) due to diving accidents were analyzed, of which 27 responded to telephone interviews. Thirty-two (97%) participants were men and 27 (81.8%) were younger than 40 years at the time of injury. The American Spinal Injury Association grade A was the most common of all grades in 16 participants (48.5%), whereas C4 was the most common neurologic level of the injury (n = 13, 39.4%). SCI due to diving accidents most commonly occurred in swimming pools in holiday lodges (n = 12, 36.4%). Five out of 13 married couples with motor complete SCI were divorced or separated after injury. Eight persons resumed work or studies after the injury, with a mean return time of 33 (24.4) months. CONCLUSIONS: SCI resulting from a diving accident not only causes severe functional impairment but can also result in changes in marital and employment status. This study may be used as a basic source of education and awareness to prevent further SCI due to diving accidents.

Weak antilocalization, spin-orbit interaction, and phase coherence length of a Dirac semimetal Bi0.97Sb0.03.

The present study develops a general framework for weak antilocalization (WAL) in a three-dimensional (3D) system, which can be applied for a consistent description of longitudinal resistivity [Formula: see text] and Hall resistivity [Formula: see text] over a wide temperature (T) range. Compared to the previous approach Vu et al. (Phys Rev B 100:125162, 2019), which assumes infinite phase coherence length (lϕ) and a zero spin-orbit scattering length (lSO), the present framework is more general, covering high T and the intermediate spin-orbit coupling strength. Based on the new approach, the [Formula: see text] and [Formula: see text] of the Dirac semimetal Bi0.97Sb0.03 was analyzed over a wide T range from 1.7 to 300 K. The present framework not only explains the main features of the experimental data but also enables one to estimate lϕ and lSO at different temperatures. The lϕ has a power-law T dependence at high T and saturates at low T. In contrast, the lSO shows negligible T dependence. Because of the different T dependence, a crossover occurs from the lSO-dominant low-T to the lϕ-dominant high-T regions. Accordingly, the hallmark features of weak antilocalization (WAL) in [Formula: see text] and [Formula: see text] are gradually suppressed across the crossover with increasing T. The present theory describes both low-T and high-T regions successfully, which is impossible in the previous approximate approach. This work offers insights for understanding quantum electrical transport phenomena and their underlying physics, particularly when multiple WAL length scales are competing.

Scattering Mechanisms and Suppression of Bipolar Diffusion Effect in Bi2Te2.85Se0.15Ix Compounds.

We investigated the anisotropic thermoelectric properties of the Bi2Te2.85Se0.15Ix (x = 0.0, 0.1, 0.3, 0.5 mol.%) compounds, synthesized by ball-milling and hot-press sintering. The electrical conductivities of the Bi2Te2.85Se0.15Ix were significantly improved by the increase of carrier concentration. The dominant electronic scattering mechanism was changed from the mixed (T ≤ 400 K) and ionization scattering (T ≥ 420 K) for pristine compound (x = 0.0) to the acoustic phonon scattering by the iodine doping. The Hall mobility was also enhanced with the increasing carrier concentration. The enhancement of Hall mobility was caused by the increase of the mean free path of the carrier from 10.8 to 17.7 nm by iodine doping, which was attributed to the reduction of point defects without the meaningful change of bandgap energy. From the electron diffraction patterns, a lattice distortion was observed in the iodine doped compounds. The modulation vector due to lattice distortion increased with increasing iodine concentration, indicating the shorter range lattice distortion in real space for the higher iodine concentration. The bipolar thermal conductivity was suppressed, and the effective masses were increased by iodine doping. It suggests that the iodine doping minimizes the ionization scattering giving rise to the suppression of the bipolar diffusion effect, due to the prohibition of the BiTe1 antisite defect, and induces the lattice distortion which decreases lattice thermal conductivity, resulting in the enhancement of thermoelectric performance.

Phonon Scattering and Suppression of Bipolar Effect in MgO/VO2 Nanoparticle Dispersed p-Type Bi0.5Sb1.5Te3 Composites.

Bismuth-Telluride-based compounds are unique materials for thermoelectric cooling applications. Because Bi2Te3 is a narrow gap semiconductor, the bipolar diffusion effect is a critical issue to enhance thermoelectric performance. Here, we report the significant reduction of thermal conductivity by decreasing lattice and bipolar thermal conductivity in extrinsic phase mixing of MgO and VO2 nanoparticles in Bi0.5Sb1.5Te3 (BST) bulk matrix. When we separate the thermal conductivity by electronic κel, lattice κlat, and bipolar κbi thermal conductivities, all the contributions in thermal conductivities are decreased with increasing the concentration of oxide particle distribution, indicating the effective phonon scattering with an asymmetric scattering of carriers. The reduction of thermal conductivity affects the improvement of the ZT values. Even though significant carrier filtering effect is not observed in the oxide bulk composites due to micro-meter size agglomeration of particles, the interface between oxide and bulk matrix scatters carriers giving rise to the increase of the Seebeck coefficient and electrical resistivity. Therefore, we suggest the extrinsic phase mixing of nanoparticles decreases lattice and bipolar thermal conductivity, resulting in the enhancement of thermoelectric performance over a wide temperature range.

Thermoelectric Properties and Low-Energy Carrier Filtering by Mo Microparticle Dispersion in an n-Type (CuI)0.003Bi2(Te,Se)3 Bulk Matrix.

We investigate the thermoelectric properties of (CuI)0.003Bi2Te2.7Se0.3/Mo (Mo: 0.0, 0.9, 1.3, 1.8, 3.1, and 4.3 vol %) composites, which were synthesized by extrinsic phase mixing with hot press sintering. From X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) measurements, we confirm that micro-sized Mo particles are dispersed homogeneously in the (CuI)0.003Bi2Te2.7Se0.3 matrix without doping. While the electrical resistivity of Mo-dispersed (CuI)0.003Bi2Te2.7Se0.3 composites is not changed significantly, the Seebeck coefficient is significantly increased. Because the work function (5.3 eV) of the (CuI)0.003Bi2Te2.7Se0.3 compounds, measured by ultraviolet photoelectron spectroscopy (UPS), is larger than that of Mo particles (4.95 eV), we expect the potential barrier near the interfaces between the BTS matrix and Mo particles. The band bending effect and potential barrier can give rise to the low-energy carrier filtering. For a low concentration dispersion of Mo particles (<2 vol %), a decrease of Hall carrier concentration, an increase of Hall mobility, a decrease of effective mass, and an increase of Seebeck coefficient also support the formation of low-energy carrier filtering. The Mo dispersion does not affect the decrease in the lattice thermal conductivity but enhances the power factor significantly, leading to the high ZT value above 1.0 at room temperature, which is a high level in n-type thermoelectric room-temperature applications.

Possible Charge Density Wave and Enhancement of Thermoelectric Properties at Mild-Temperature Range in n-Type CuI-Doped Bi2Te2.1Se0.9 Compounds.

Bi2Te3-based compounds have long been studied as thermoelectric materials in cooling applications near room temperature. Here, we investigated the thermoelectric properties of CuI-doped Bi2Te2.1Se0.9 compounds. The Cu/I codoping induces the lattice distortion partially in the matrix. We report that the charge density wave caused by the local lattice distortion affects the electrical and thermal transport properties. From the high-temperature specific heat, we found a first-order phase transitions near 490 and 575 K for CuI-doped compounds (CuI)xBi2Te2.1Se0.9 (x = 0.3 and 0.6%), respectively. It is not a structural phase transition, confirming from the high-temperature X-ray diffraction. The temperature-dependent electrical resistivity shows a typical behavior of charge density wave transition, which is consistent with the temperature-dependent Seebeck coefficient and thermal conductivity. The transmission electron microscopy and electron diffraction show a local lattice distortion, driven by the charge density wave transition. The charge density wave formation in the Bi2Te3-based compounds are exceptional because of the possibility of coexistence of charge density wave and topological surface states. From the Kubo formula and Boltzmann transport calculations, the formation of charge density wave enhances the power factor. The lattice modulation and charge density wave decrease lattice thermal conductivity, resulting in the enhancement of thermoelectric performance simultaneously in CuI-doped samples. Consequently, an enhancement of thermoelectric performance ZT over 1.0 is achieved at 448 K in the (CuI)0.003Bi2Te2.1Se0.9 sample. The enhancement of ZT at high temperature gives rise to a superior average ZTavg (1.0) value than those of previously reported ones.

Synergetic Enhancement of Thermoelectric Performance by Selective Charge Anderson Localization-Delocalization Transition in n-Type Bi-Doped PbTe/Ag2Te Nanocomposite.

Considerable efforts have been devoted to enhancing thermoelectric performance, by employing phonon scattering from nanostructural architecture, and material design using phonon-glass and electron-crystal concepts. The nanostructural approach helps to lower thermal conductivity but has limited effect on the power factor. Here, we demonstrate selective charge Anderson localization as a route to maximize the Seebeck coefficient while simultaneously preserving high electrical conductivity and lowering the lattice thermal conductivity. We confirm the viability of interface potential modification in an n-type Bi-doped PbTe/Ag2Te nanocomposite and the resulting enhancement in thermoelectric figure-of-merit ZT. The introduction of random potentials via Ag2Te nanoparticle distribution using extrinsic phase mixing was determined using scanning tunneling spectroscopy measurements. When the Ag2Te undergoes a structural phase transition ( T > 420 K) from monoclinic ß-Ag2Te to cubic α-Ag2Te, the band gap in the α-Ag2Te increases due to the p -d hybridization. This results in a decrease in the potential barrier height, which gives rise to partial delocalization of the electrons, while wave packets of the holes are still in a localized state. Using this strategic approach, we achieved an exceptionally high thermoelectric figure-of-merit in n-type PbTe materials, a ZT greater than 2.0, suitable for waste heat power generation.

Enhancement of Thermoelectric Performance in Na-Doped Pb0.6Sn0.4Te0.95- xSe xS0.05 via Breaking the Inversion Symmetry, Band Convergence, and Nanostructuring by Multiple Elements Doping.

Topological insulators have attracted much interest in topological states of matter featuring unusual electrical conduction behaviors. It has been recently reported that a topological crystalline insulator could exhibit a high thermoelectric performance by breaking its crystal symmetry via chemical doping. Here, we investigate the multiple effects of Na, Se, and S alloying on thermoelectric properties of a topological crystalline insulator Pb0.6Sn0.4Te. The Na doping is known to be effective for breaking the crystalline mirror symmetry of Pb0.6Sn0.4Te. We demonstrate that simultaneous emergence of band convergence by Se alloying and nanostructuring by S doping enhance the power factor and decrease lattice thermal conductivity, respectively. Remarkably, the high power factor of 22.3 µW cm-1 K-2 at 800 K is achieved for Na 1%-doped Pb0.6Sn0.4Te0.90Se0.05S0.05 mainly due to a relatively high Seebeck coefficient via band convergence by Se alloying as well as the suppression of bipolar conduction at high temperatures by the increase of energy band gap. Furthermore, the lattice thermal conductivity is significantly suppressed by PbS nanoprecipitates without deteriorating the hole carrier mobility, ranging from 0.80 W m-1 K-1 for Pb0.6Sn0.4Te to 0.17 W m-1 K-1 at 300 K for Pb0.6Sn0.4Te0.85Se0.10S0.05. As a result, the synergistically combined effects of breaking the crystalline mirror symmetry of topological crystalline insulator, band convergence, and nanostructuring for Pb0.6Sn0.4Te0.95- xSe xS0.05 ( x = 0, 0.05, 0.1, 0.2, and 0.95) give rise to an impressively high ZT of 1.59 at 800 K for x = 0.05. We suggest that the multiple doping in topological crystalline insulators is effective for improving the thermoelectric performance.