We demonstrate that a single zone furnace with a modified synthesis chamber design is sufficient to obtain metal (Fe, Co or Ni) filled carbon nanotubes (CNT) with high filling efficiency and controlled morphology. Samples are formed by pyrolysis of metallocenes, a synthesis technique that otherwise requires a dual zone furnace. Respective metallocene in all three cases are sublimed in powder form, a crucial factor for obtaining high filling efficiency.While Fe@CNT is routinely produced using this technique, well-formed Ni@CNT orCo@CNT samples are reported for the first time. This is achieved by sublimation of nickelocene (or cobaltocene) in combination with 'camphor'. These samples exhibit some of the highest saturation magnetization (Ms) values, at least an order of magnitude higher than that reported for Ni or Co@CNT, by aerosol assisted pyrolysis. The results also elucidate on why Ni or Co@CNT are relatively difficult to obtain by pyrolyzing powder metallocene 2 alone. Overall, a systematic variation of synthesis parameters provides insights for obtaining narrow length and diameter distribution and reduced residue particles outside filled CNTfactors which are important for device related applications. Finally, the utility of this technique is demonstrated by obtaining highly aligned forest of Fe2O3@CNT, wherein Fe2O3 is a functional magnetic oxide relevant to spintronics and battery applications.

Downsizing well-established materials to the nanoscale is a key route to novel functionalities, in particular if different functionalities are merged in hybrid nanomaterials. Hybrid carbon-based hierarchical nanostructures are particularly promising for electrochemical energy storage since they combine benefits of nanosize effects, enhanced electrical conductivity and integrity of bulk materials. We show that endohedral multiwalled carbon nanotubes (CNT) encapsulating high-capacity (here: conversion and alloying) electrode materials have a high potential for use in anode materials for lithium-ion batteries (LIB). There are two essential characteristics of filled CNT relevant for application in electrochemical energy storage: (1) rigid hollow cavities of the CNT provide upper limits for nanoparticles in their inner cavities which are both separated from the fillings of other CNT and protected against degradation. In particular, the CNT shells resist strong volume changes of encapsulates in response to electrochemical cycling, which in conventional conversion and alloying materials hinders application in energy storage devices.(2) Carbon mantles ensure electrical contact to the active material as they are unaffected by potential cracks of the encapsulate and form a stable conductive network in the electrode compound. Our studies confirm that encapsulates are electrochemically active and can achieve full theoretical reversible capacity. The results imply that encapsulating nanostructures inside CNT can provide a route to new high-performance nanocomposite anode materials for LIB.

The interface of two dissimilar materials is well known for surprises in condensed matter, and provides avenues for rich physics as well as seeds for future technological advancements.We present some exciting magnetization (M) and remnant magnetization (µ) results, which conclusively arise at the interface of two highly functional materials, namely the graphitic shells of a carbon nanotube (CNT) and α-Fe2O3, a Dzyaloshinskii-Moriya Interaction (DMI) driven weak ferromagnet (WFM) and piezomagnet (PzM). We show that the encapsulation inside CNT leads to a very significant enhancement in M and correspondingly in µ, a time-stable part of the remanence, exclusive to the WFM phase. Up to 70% of in-field magnetization is retained in the form of µ at the room temperature. Lattice parameter of CNT around the Morin transition of the encapsulate exhibits a clear anomaly, confirming the novel interface effects. Control experiments on bare α-Fe2O3 nanowires bring into fore that the weak ferromagnets such as α-Fe2O3 as are not as weak, as far as their remanence and its stability with time is concerned, and encapsulation inside CNT leads to a substantial enhancement in these functionalities.Hematite (or α-Fe2O3) is an earth abundant and environment-friendly oxide, generally considered as a menace, for its appearance as common rust over elemental Fe, but technologically, it is well known for a very diverse range of applications. [1] However, the observation of WFM [2,3] nearly six decades ago in hematite and its connection to spin orbit coupling (SOC) has had profound implications in the field of spintronics. A variety of nontrivial topological spin structures in chiral magnets stabilizing through DMI/SOC have triggered new research areas such as antiferromagnetic spintronics and spin orbitronics [4,9] .Generation of WFM in α-Fe2O3 is due to a slight canting of its inherent AFM sublattice [2,3] which persists from 950 K (TN) down to 265 K, well-known Morin Transition temperature (TM). Below TM, the spins turn from "a" axis to "c" axis (rhombohedral unit cell in hex setting) and the canting vanishes for hematite. Many of such canted AFM, either DMI driven or systems in which canting takes place due to other mechanism, are also known to exhibit the phenomenon of piezomagnetism. [10,14] Here, PzM implies that magnetization can be tuned by stress alone.Another important point is the occurrence of WFM which is concurrent with PzM as theoretically predicted [10] and experimentally observed [11,14] . Dzyaloshinskii also showed that the spin canting effect is larger for compounds with smaller TN [2] . Thus, WFM / PzM is seen to be the weakest in α-Fe2O3 with TN ~950 K as compared to MnCO3 or NiCO3 (TN below 50 K).This work centers around remanence µ, which, in general, is an important parameter for any magnetic material for a variety of practical applications related to permanent magnets, soft or hard, relate to this quantity [15,17] . In addition, it is an important tool for probing fundamental magnetic interactions in conventional lon...

We report a comparative study on the electrochemical performance of four different Transition Metal Oxides encapsulated inside carbon nanotubes (Oxide@CNT), along with a reference data obtained on a bare-oxide. A key result here is that the encapsulation leads to superior cyclic stability, irrespective of the type of the oxide-encapsulate. This comparison also enables us to isolate the advantages associated with the encapsulation of oxide within the core cavity of CNT, as opposed to the case of oxide/CNT composites, in which oxide resides outside the CNT. Innovative use of camphor during sample synthesis enables precise control over the morphology of the filled CNT, which can be either in aligned-forest or in entangled geometry. Morphology appears to play a crucial role in tuning the magnitude of the specific capacity, whereas the encapsulation relates to the cyclic stability. Overall, the electrochemical data on various Oxides@CNT bring forward interesting inferences pertaining to the morphology, filling fraction of the oxide-encapsulate, and the presence of oxide nano-particles adhering outside the CNT. Our results provides useful pointers for optimization of these critical parameters, thus paving the way for Oxide@CNT for practical electrochemical applications.