Superparamagnetic-like behaviour in RE2WO6 tungstates (where RE = Nd, Sm, Eu, Gd, Dy, Ho and Er)

The magnetization isotherms were used to study the superparamagnetic-like behaviour in polycrystalline (powder) RE2WO6 tungstates (where RE = Nd, Sm, Eu, Gd, Dy, Ho and Er). The magnetization isotherms of the majority tungstates under study revealed both the spontaneous magnetic moments and hysteresis characteristic for the superparamagnetic-like behaviour with blocking temperature TB ¼ 30 K except the Sm2WO6 and Eu2WO6 compounds

Discovering a Defect that Imposes a Limit to Mg Doping in p-TypeGaN

Gallium nitride (GaN) is the III-V semiconductor used to produce blue light-emitting diodes (LEDs) and blue and ultraviolet solid-state lasers. To be useful in electronic devices, GaN must be doped with elements that function either as electron donors or as acceptors to turn it into either an n-type semiconductor or a p-type semiconductor. It has been found that GaN can easily be grown with n-conductivity, even up to large concentrations of donors--in the few 10{sup 19}cm{sup -3} range. However, p-doping, the doping of the structure with atoms that provide electron sinks or holes, is not well understood and remains extremely difficult. The only efficient p-type dopant is Mg, but it is found that the free hole concentration is limited to 2 x 10{sup 18}cm{sup -3}, even when Mg concentrations are pushed into the low 10{sup 19}cm{sup -3} range. This saturation effect could place a limit on further development of GaN based devices. Further increase of the Mg concentration, up to 1 x 10{sup 20}cm{sup -3} leads to a decrease of the free hole concentration and an increase in defects. While low- to medium-brightness GaN light-emitting diodes (LEDs) are remarkably tolerant of crystal defects, blue and UV GaN lasers are much less so. We used electron microscopy to investigate Mg doping in GaN. Our transmission electron microscopy (TEM) studies revealed the formation of different types of Mg-rich defects [1,2]. In particular, high-resolution TEM allowed us to characterize a completely new type of defect in Mg-rich GaN. We found that the type of defect depended strongly on crystal growth polarity. For crystals grown with N-polarity, planar defects are distributed at equal distances (20 unit cells of GaN); these defects can be described as inversion domains [1]. For growth with Ga-polarity, we found a different type of defect [2]. These defects turn out to be three-dimensional Mg-rich hexagonal pyramids (or trapezoids) with their base on the (0001) plane and their six walls formed on {l_brace}1123{r_brace} planes (Fig. 1a). In [1120] and [1100] cross-section TEM micrographs the defects appear as triangular (Fig. 1b) and trapezoidal (Fig. 1c). In projection, the sides of these defects are inclined at 43{sup o} and 47{sup o} to the base depending on the observation direction. The pyramid size varies from 50{angstrom}-1000{angstrom} depending on the growth method, but the angle between the base and sides remain the same. The direction from the tip of the pyramid to its base (and from the shorter to the longer base for trapezoidal defects) is along the Ga to N matrix bond direction (Fig. 1a-d)

Defects in p-GaN and their atomic structure

In this paper defects formed in p-doped GaN:Mg grown with Ga polarity will be discussed. The atomic structure of these characteristic defects (Mg-rich hexagonal pyramids and truncated pyramids) in bulk and thin GaN:Mg films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects. The inside walls of the cavities were covered by GaN which grew with reverse polarity compared to the matrix. It was proposed that lateral overgrowth of the cavities restores matrix polarity on the defect base. Exchange of Ga and N sublattices within the defect compared to the matrix lead to a 0.6 {+-} 0.2 {angstrom} displacement between the Ga sublattices of these two areas. A [1{und 1}00]/3 shift with change from AB stacking in the matrix to BC within the entire pyramid is observe

Atomic Structure of Pyramidal Defects in GaN:Mg; Influence ofAnnealing

The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and MOCVD GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, confirmed also with positron annihilation. The inside walls of the cavities were covered by GaN of reverse polarity compared to the matrix. Defects in bulk GaN:Mg were almost one order of magnitude larger than in thin films. An exchange of Ga and N sublattices within the defect compared to the matrix lead to a 0.6 {+-} 0.2 {angstrom} displacement between the Ga sublattices of these two areas. A [1100]/3 shift with change from AB stacking in the matrix to BC within the entire pyramid was observed. Annealing of the MOCVD layers lead to slight increase of the defect size and an increase of the photoluminescence intensity. Positron annihilation confirms presence of vacancies of different sizes triggered by the Mg doping in as-grown samples and decrease of their concentration upon annealing at 900 and 1000 C

Basic chemical properties and contents of Pb, Zn, Cu, Ni, Cd in soils on area of former iron foundry and non-ferrous metals in Nowogard (West Pomeranian Province)

Celem pracy była ocena podstawowych właściwości chemicznych i ogólnej zawartości Pb, Zn, Cu, Ni i Cd w poziomie próchnicznym gleb z terenu byłej odlewni żeliwa i metali kolorowych w Nowogardzie (woj. zachodniopomorskie). Zakład ten nie działa od ok. 10 lat, a jego teren obecnie w dużym stopniu pokryty jest gruzem z niszczejących budynków i innymi nielegalnie składowanymi odpadami. Stwierdzono, że badane gleby były zasadowe, a ich niskie zasolenie wynika z luźnego uziarnienia. Maksymalna zawartość metali wynosiła: 467,4 dla Pb; 546,0 dla Zn; 452,0 dla Cu; 64,9 dla Ni i 4,45 mgxkg-1 dla Cd. Zawartości wyższe od dopuszczonych prawem dla gruntów zabudowanych i zurbanizowanych odnotowano dla Zn, Cu, Pb i Cd. Wzbogacenie gleb w Ni było nieznaczne i nie wskazywało na zanieczyszczenie. Uwzględniając aktualną jakość gleb i lokalizację terenu w obrębie Nowogardu, racjonalnym sposobem jego zagospodarowania byłoby przeznaczenie do działalności produkcyjnej (drobna wytwórczość), składowania i magazynowania. Teren ten po-winien być w jak największym stopniu zadarniony i otoczony pasem drzew i krzewów, by ograniczyć migrację metali w środowisku przez fitostabilizację i zmniejszenie ryzyka erozji. Takie działanie uzasadnia luźne uziarnienie gleb i fakt istnienia w niedalekim sąsiedztwie doliny ze zbiorowiskami szuwarowymi podmokłych łąk.The aim of this work was assessment of basic chemical properties and Pb, Zn, Cu, Ni, Cd total content in soil humus horizon from area of former iron foundry and non-ferrous metals in Nowogard (West Pomeranian Province). This foundry does not work from approx. 10 years and the ar-ea now largely covered by the rubble of crumbling buildings and other waste of stored illegally. It was found that the investigated soils had alkaline character and their low salinity was the result of loose texture. The maximum contents of metals were: 467.4 for Pb, 546.0 for Zn, 452.0 for Cu, 64.9 for Ni and 4.45 mgxkg-1 for Cd. Content higher than permitted by law for built-up urban areas reported for Zn, Cu, Pb and Cd. Soil enrichment in Ni was low and no sign of contamination. Given the current soil quality and location of former foundry on the Nowogard area, rational way will been to allocate this terrain to productive activities (small production), storage and warehousing. This area should be in high degree covered with grasses and surrounded by a belt of dense trees and shrubs to reduce the migration of metals in the environment by phytostabilization and minimize the risk of erosion. This action would be desirable considering the loose texture of soils and the existence in the vicinity of the valley with the communities of rushes and wet meadows

Content of heavy metals in anthropogenic sediments from area of old town Szczecin

W pracy scharakteryzowano osady antropogeniczne z obszaru Starego Miasta Szczecina (Placu Orła Białego), których warstwa osiąga grubość ok. 4 m, a materiały w niej zawarte wzbogacone są w materię organiczną, w tym próchnicę. Osady te zawierają ogromną ilość zanieczyszczeń mechanicznych, wśród których dominują odpady gruzu budowlanego tworzące, w zasięgu warstwy antropogenicznej, 3-metrową ciągłą warstwę typowo gruzową. Gruz budowlany wzbogacił grunty w węglan wapnia i spowodował ich alkalizację, nawet do poziomu pHKCl=8,7. Spowodował także bardzo wyraźny wzrost zawartości ołowiu i cynku, wyraźny - miedzi i w niewielkim stopniu wzbogacił osady w kadm. Nie potwierdzono wpływu domieszek na zawartość niklu. Maksymalne zawartości Zn, Cu, Pb i Cd wynosiły odpowiednio: 685, 146, 716 i 1,7 mg x kg-1 i były to ilości przekraczające dopuszczalny poziom dla I grupy gruntów: siedmiokrotnie w od-niesieniu do ołowiu i dwukrotnie w przypadku cynku według Rozporządzenia Ministra Środowiska z dnia 1 września 2016 roku [Dz.U. 2016 nr 0 poz. 1395].In this work the anthropogenic sediments from area of Old Town Szczecin (Square of Orła Białego) were characterized. It was found that layer of these sediments had thickness of approx. 4 m and materials contained therein were enriched in organic matter, including humus. These sediments contained a huge amount of mechanical deposits which were dominated by building rubble that formed of 3-meter continuous rubble layer within the anthropogenic layer. Building rubble enriched materials in calcium carbonate and caused their alkalinisation even to level pHKCl=8.7. These deposits caused also a very clear increase of lead and zinc contents, clear increase of copper content and slightly enrichment of materials in cadmium. Not confirmed the effect of mechanical deposits on nickel content. The maximum content of Zn, Cu, Pb and Cd were respectively: 685, 146, 716 and 1.7 mg x kg-1. These amounts were higher than acceptable level for I group of grounds: seven times in respect of lead, twice in case of zinc according Regulation of Minister of Environment from 1 September 2016 [Dz.U. 2016 nr 0 poz. 1395]