Penerapan Metode Pembelajaran Numbered Heads Together (Nht) Untuk Meningkatkan Motivasi Dan Hasil Belajar Kelarutan Dan Hasil Kali Kelarutan Kelas XI IPA 4 Sman 8 Surakarta Tahun Pelajaran 2012/2013

Tujuan penelitian ini adalah untuk meningkatkan (1) motivasi belajar kelarutan dan hasil kali kelarutan dan (2) hasil belajar kelarutan dan hasil kali kelarutan melalui penerapan metode pembelajaran Numbered Heads Together (NHT). Penelitian ini merupakan penelitian tindakan kelas (Classroom Action Research) yang dilaksanakan dalam dua siklus dimana setiap siklusnya terdiri atas empat tahapan, yaitu perencanaan, pelaksanaan, pengamatan, dan refleksi. Subjek penelitian adalah siswa kelas XI IPA 4 SMAN 8 Surakarta Tahun Pelajaran 2012/2013. Pengumpulan data dilakukan melalui pengamatan, wawancara, kajian dokumen, angket, dan tes. Data yang diperoleh divalidasi menggunakan teknik triangulasi sumber dan dianalisis menggunakan analisis deskriptif kualitatif yang mengacu pada Miles dan Huberman. Hasil penelitian menunjukkan capaian motivasi belajar pada siklus I dan siklus II masing-masing mencapai 58,33% dan 79,17%. Hasil belajar yang diukur pada aspek kognitif dan afektif menunjukkan pada siklus I mencapai 29,17% dan 62,5% serta pada siklus II mencapai 70,83% dan 83,33%. Simpulan penelitian ini adalah penerapan metode pembelajaran Numbered Heads Together (NHT) mampu meningkatkan (1) motivasi belajar kelarutan dan hasil kali kelarutan dan (2) hasil belajar kelarutan dan hasil kali kelarutan kelas XI IPA 4 SMAN 8 Surakarta

Topological Surface State Annihilation and Creation in SnTe/Cr_<i>x</i>(BiSb)_2–<i>x</i>Te₃ Heterostructures

Topological surface states are a new class of electronic states with novel properties, including the potential for annihilation between surface states from two topological insulators at a common interface. Here, we report the annihilation and creation of topological surface states in the SnTe/Crx(BiSb)2–xTe3 (CBST) heterostructures as evidenced by magneto-transport, polarized neutron reflectometry, and first-principles calculations. Our results show that topological surface states are induced in the otherwise topologically trivial two-quintuple-layers thick CBST when interfaced with SnTe, as a result of the surface state annihilation at the SnTe/CBST interface. Moreover, we unveiled systematic changes in the transport behaviors of the heterostructures with respect to changing Fermi level and thickness. Our observation of surface state creation and annihilation demonstrates a promising way of designing and engineering topological surface states for dissipationless electronics

Coalescence in the Thermal Annealing of Nanoparticles: An in Situ STEM Study of the Growth Mechanisms of Ordered Pt–Fe Nanoparticles in a KCl Matrix

Thermal annealing is essential for achieving ultrasmall size ferromagnetic properties in next-generation high performance nanocomposite magnetic materials. However, during the annealing process, growth and agglomeration of nanoparticles normally occurs, which destroys the narrow size distributions. Thus, the materials become less suitable for application in high-density magnetic recording. The mechanism of nanoparticle growth and sintering has been difficult to determine because of the lack of suitable in situ tools to probe subnanometer changes at the local level. Here we report a study using high-resolution scanning transmission electron microscopy (STEM) coupled with an in situ thermal annealing stage of surfactant-free, monodispersed superparamagnetic PtFe (cubic) alloy nanoparticles (≈2 nm in diameter) stabilized in or on a KCl matrix. Ex situ experiments confirmed that annealing produces PtFe (tetragonal) ordered intermetallic nanoparticles with a mean diameter of 5 nm, and the in situ study revealed that the mechanism of nanoparticle growth is dominated by particle–particle coalescence, although Ostwald ripening is also implicated in a few regions. In addition, to determine the time dependent evolution of the size distribution of an ensemble of over 400 nanoparticles, analysis of the in situ data also allows tracking of individual nanoparticles, distinguishing coalescence from Ostwald ripening, nanoparticle by nanoparticle. This approach has provided valuable insights into changes in crystal structure and sintering that occur during the thermal annealing of Pt–Fe nanoparticles

Emergent Ferromagnetism in CaRuO₃/CaMnO₃ (111)-Oriented Superlattices

The boundary between CaRuO3 and CaMnO3 is an ideal test bed for emergent magnetic ground states stabilized through interfacial electron interactions. In this system, nominally antiferromagnetic and paramagnetic materials combine to yield interfacial ferromagnetism in CaMnO3 due to electron leakage across the interface. In this work, we show that the crystal symmetry at the surface is a critical factor determining the nature of the interfacial interactions. Specifically, by growing CaRuO3/CaMnO3 heterostructures along the (111) instead of the (001) crystallographic axis, we achieve a 3-fold enhancement of the magnetization and involve the CaRuO3 layers in the ferromagnetism, which now spans both constituent materials. The stabilization of a net magnetic moment in CaRuO3 through strain effects has been long-sought but never consistently achieved, and our observations demonstrate the importance of interface engineering in the development of new functional heterostructures

High-Throughput Selection and Experimental Realization of Two New Ce-Based Nitride Perovskites: CeMoN₃ and CeWN₃

Nitride perovskites have only been experimentally realized in very few cases despite the widespread existence and commercial importance of perovskite materials. From oxide perovskites used in ultrasonics to halide perovskites that have revolutionized the photovoltaics industry, the discovery of new perovskite materials has historically impacted a wide number of fields. Here, we add two new perovskites, CeWN3 and CeMoN3, to the list of experimentally realized perovskite nitrides using high-throughput computational screening and subsequent high-throughput thin film growth techniques. Candidate compositions are first down-selected using a tolerance factor and then thermochemical stability. A novel competing fluorite-family phase is identified for both material systems, which we hypothesize is a transient intermediate phase that crystallizes during the evolution from an amorphous material to a stable perovskite. Different processing routes to overcome the competing fluorite phase and obtain phase-pure nitride perovskites are demonstrated for the CeMoN3–x and CeWN3–x material systems, which provide a starting point for the development of future nitride perovskites. Additionally, we find that these new perovskite phases have interesting low-temperature magnetic behavior: CeMoN3–x orders antiferromagnetically below TN ≈ 8 K with indications of strong magnetic frustration, while CeWN3–x exhibits no long-range order down to T = 2 K but has strong antiferromagnetic correlations. This work demonstrates the importance and effectiveness of using high-throughput techniques, both computational and experimental: they are integral to optimize the process of realizing two entirely novel nitride perovskites

High-Throughput Selection and Experimental Realization of Two New Ce-Based Nitride Perovskites: CeMoN₃ and CeWN₃

Nitride perovskites have only been experimentally realized in very few cases despite the widespread existence and commercial importance of perovskite materials. From oxide perovskites used in ultrasonics to halide perovskites that have revolutionized the photovoltaics industry, the discovery of new perovskite materials has historically impacted a wide number of fields. Here, we add two new perovskites, CeWN3 and CeMoN3, to the list of experimentally realized perovskite nitrides using high-throughput computational screening and subsequent high-throughput thin film growth techniques. Candidate compositions are first down-selected using a tolerance factor and then thermochemical stability. A novel competing fluorite-family phase is identified for both material systems, which we hypothesize is a transient intermediate phase that crystallizes during the evolution from an amorphous material to a stable perovskite. Different processing routes to overcome the competing fluorite phase and obtain phase-pure nitride perovskites are demonstrated for the CeMoN3–x and CeWN3–x material systems, which provide a starting point for the development of future nitride perovskites. Additionally, we find that these new perovskite phases have interesting low-temperature magnetic behavior: CeMoN3–x orders antiferromagnetically below TN ≈ 8 K with indications of strong magnetic frustration, while CeWN3–x exhibits no long-range order down to T = 2 K but has strong antiferromagnetic correlations. This work demonstrates the importance and effectiveness of using high-throughput techniques, both computational and experimental: they are integral to optimize the process of realizing two entirely novel nitride perovskites

High-Throughput Selection and Experimental Realization of Two New Ce-Based Nitride Perovskites: CeMoN₃ and CeWN₃

Nitride perovskites have only been experimentally realized in very few cases despite the widespread existence and commercial importance of perovskite materials. From oxide perovskites used in ultrasonics to halide perovskites that have revolutionized the photovoltaics industry, the discovery of new perovskite materials has historically impacted a wide number of fields. Here, we add two new perovskites, CeWN3 and CeMoN3, to the list of experimentally realized perovskite nitrides using high-throughput computational screening and subsequent high-throughput thin film growth techniques. Candidate compositions are first down-selected using a tolerance factor and then thermochemical stability. A novel competing fluorite-family phase is identified for both material systems, which we hypothesize is a transient intermediate phase that crystallizes during the evolution from an amorphous material to a stable perovskite. Different processing routes to overcome the competing fluorite phase and obtain phase-pure nitride perovskites are demonstrated for the CeMoN3–x and CeWN3–x material systems, which provide a starting point for the development of future nitride perovskites. Additionally, we find that these new perovskite phases have interesting low-temperature magnetic behavior: CeMoN3–x orders antiferromagnetically below TN ≈ 8 K with indications of strong magnetic frustration, while CeWN3–x exhibits no long-range order down to T = 2 K but has strong antiferromagnetic correlations. This work demonstrates the importance and effectiveness of using high-throughput techniques, both computational and experimental: they are integral to optimize the process of realizing two entirely novel nitride perovskites

Stromataxic Stabilization of a Metastable Layered ScFeO₃ Polymorph

Metastable polymorphsmaterials with the same stoichiometry as the ground state but a different crystal structure enable many critical technologies. This work describes the development of a stabilization approach for metastable polymorphs that are difficult to achieve through other stabilization techniques (such as epitaxy or quenching) called stromataxy. Stromataxy is a method based on controlling the precursor structure during the initial stages of material growth to dictate phase formation. To illustrate this approach, we controlled the atomic layering of the precursors of ScFeO3 and stabilized the metastable P63cm phase, under conditions that previously led to the ground-state Ia3̅ bixbyite phase. Ab initio mechanistic calculations highlight the importance of the variable oxidation state of Fe and the layer stability during layer-by-layer growth. The broad applicability of a stromataxy approach was demonstrated by stabilizing this metastable phase on substrates that have previously been shown to stabilize other polymorphs under continuous growth. Stromataxy is shown as a viable option for accessing polymorphs that are close in energy, difficult to differentiate by strain, or that lack a well epitaxially matched substrate

Conductivity and Microstructure of Combinatorially Sputter-Deposited Ta–Ti–Al Nitride Thin Films

Materials with long-term durability and electrical conductivity at low pH (<2) and high potentials (∼1.4 V vs RHE) are of great interest as catalyst supports in proton exchange membrane (PEM) fuel cells. We have evaluated Ta–Ti–Al nitrides for this purpose. Combinatorial sputter-deposition of Ta–Ti–Al nitride thin films allowed the composition of these films to be varied spatially over a substrate at ∼1 atomic %/mm, enabling the investigation of the conductivity and microstructure of these materials over a wide range of compositions. Conductive probe atomic force microscopy (cp-AFM) is shown to facilitate high-throughput screening of electrical conductivity as a function of composition. Local, tip-induced oxidation of the film indicated that films annealed in the presence of oxygen were most resistant to oxidation-induced losses of conductivity. Ti-rich compositions exhibited conductivities similar to carbon black and best retained their conductivity after tip-induced oxidation. Small amounts of Ti (∼20 atomic %) were sufficient to impart desired conductivities to compositions rich in Ta and Al, which without Ti exhibited insulating behavior. Electron energy-loss spectroscopy (EELS) imaging revealed the formation of a <2 nm oxide layer at the surface of the nitride films, which is expected to make these materials more durable. Remarkably, high conductivities were observed in the presence of this oxide layer. Segregation of elements was observed at sub-10-nm length scales, yet mapping the lattice constant of the film with X-ray diffraction showed that the majority phase is a well-mixed alloy with a lattice constant that varies smoothly over the entire range of compositions. The rock-salt structure was observed at all compositions except those with high levels of Al

Ferroelectric Domain Walls in PbTiO₃ Are Effective Regulators of Heat Flow at Room Temperature

Achieving efficient spatial modulation of phonon transmission is an essential step on the path to phononic circuits using “phonon currents”. With their intrinsic and reconfigurable interfaces, domain walls (DWs), ferroelectrics are alluring candidates to be harnessed as dynamic heat modulators. This paper reports the thermal conductivity of single-crystal PbTiO3 thin films over a wide variety of epitaxial-strain-engineered ferroelectric domain configurations. The phonon transport is proved to be strongly affected by the density and type of DWs, achieving a 61% reduction of the room-temperature thermal conductivity compared to the single-domain scenario. The thermal resistance across the ferroelectric DWs is obtained, revealing a very high value (≈5.0 × 10–9 K m2 W–1), comparable to grain boundaries in oxides, explaining the strong modulation of the thermal conductivity in PbTiO3. This low thermal conductance of the DWs is ascribed to the structural mismatch and polarization gradient found between the different types of domains in the PbTiO3 films, resulting in a structural inhomogeneity that extends several unit cells around the DWs. These findings demonstrate the potential of ferroelectric DWs as efficient regulators of heat flow in one single material, overcoming the complexity of multilayers systems and the uncontrolled distribution of grain boundaries, paving the way for applications in phononics