O grupo de diboretos isoestruturais ao MgB2 com estrutura representada pelo protótipo AlB2 é considerado candidato à supercondutividade. Contudo, a existência do estado supercondutor é um fenômeno raro nesse grupo de materiais, de fato a grande maioria dos diboretos de metais de transição é caracterizada por um Tc menor que 0,7 K. Nesse grupo, os compostos normais HfB2, VB2, YB2 e ZrB2 exibem assinatura do comportamento paramagnético de Pauli em baixas temperaturas. Nesse trabalho é mostrado que a substituição parcial do metal (Hf e Zr) por V nas amostras M1-xVxB2, gera distorções da rede cristalina, com o surgimento de um estado supercondutor volumétrico. As medidas magnéticas, elétricas e térmicas revelam um Tc máximo atingindo 8,7 e 9,3 K para as respectivas amostras de composição Zr0,96V0,04B2 e Hf0,97V0,03B2, com valores elevados de ? 0Hc2(0) (~16 e ~21 T, respectivamente). Nessas amostras, os resultados a cerca do comportamento do ? 0Hc1 (T), do Cp(T) e da VHall (T), e medidas de ETS (electronic tunneling spectroscopy) em um monocristal, revelam a claras assinaturas da supercondutividade multibanda, tal como é reportado para o MgB2. Ainda, resultados mostram a que a existência do estado supercondutor no ZrB2 parece não ser uma exclusividade da substituição por V, já que é observada também na amostra de Zr0,96Y0,04B2, cujo Tc atinge 6,7 K novamente com assinatura de comportamento multibanda. Também são mostrados os resultados da existência dos comportamentos magnéticos competitivos nas amostras do sistema Zr1-xAlxB2, com um surpreendente ordenamento ferromagnético. Nesse mesmo cenário, também é mostrado que substituição de Nb por Ni é hábil em elevar a temperatura crítica do composto NbB2-? de 3,6 K para 6,0 K. Já em outros boretos, como nos sistemas Th1-xMxB12 (M = Zr, Sc, Y, Ti Hf) em condições especiais de síntese e substituição a fase ThB12 (inexistente no equilíbrio) pode ser estabilizada, onde se observa para amostra Th0,97Zr0,03B12 um Tc próximo a 5,5 K e comportamento supercondutor BCS, porém com um baixo valor do parâmetro k o que abre discussão para uma classe nova de supercondutores do tipo 1,5. / The diborides group isostructural to MgB2 represented by AlB2 prototype structure are considered important candidates for superconductivity. However, the existence of the superconducting state is a rare phenomenon in this group of materials, indeed the majority of transition metal diborides are characterized by a Tc lower than 0.7 K. In this group, the normal compounds HfB2, VB2, YB2, and ZrB2 exhibit signature Pauli paramagnetic behavior at low temperatures. In this work it is shown that the metal partial substitution (Hf and Zr) by V in M1-xVxB2 samples generates distortions of the crystal lattice, with the emergence of a bulk superconducting state. The magnetic, electric and thermal measurements reveal a maximum Tc reaching 8.7 and 9.3 K for the respective samples Zr0.96V0.04B2 and Hf0.97V0.03B2 composition with high values of ? 0Hc2(0) (~ 16 and ~ 21 T, respectively). In these samples, the results about the behavior ? 0Hc1 (T), Cp(T), and VHall (T); and ETS (electronic tunneling spectroscopy) measurements in a single crystal; reveal a clear signatures of multiband superconductivity such as reported to the MgB2. Furthermore, the results show that the existence of the superconducting state ZrB2 appears to be not exclusive by V substitution, it is also observed in the sample Zr0.96Y0.04B2 whose Tc reaches 6.7 K again with signature multiband behavior. Also shown are the results of the existence of competitive magnetic behavior in samples of Zr1-xAlxB2 system, with a surprising ferromagnetic ordering. In this same scenario, it is also shown that substitution of Nb by Ni is able to raise the critical temperature of the NbB2-? compound from 3.6 K to 6.0 K. Since other borides as in Th1- xMxB12 (M = Zr, Sc, Y, Ti Hf) systems, in special conditions of synthesis and substitution the ThB12 phase (non-existent in the equilibrium conditions) can be stabilized, which is observed to Th0.97Zr0.03B12 sample with Tc close to 5.5 K and BCS superconducting behavior, but with a low of the k parameter value opening discussion for a new class of 1.5 type superconductors.

O grupo de diboretos isoestruturais ao MgB2 com estrutura representada pelo protótipo AlB2 é considerado candidato à supercondutividade. Contudo, a existência do estado supercondutor é um fenômeno raro nesse grupo de materiais, de fato a grande maioria dos diboretos de metais de transição é caracterizada por um Tc menor que 0,7 K. Nesse grupo, os compostos normais HfB2, VB2, YB2 e ZrB2 exibem assinatura do comportamento paramagnético de Pauli em baixas temperaturas. Nesse trabalho é mostrado que a substituição parcial do metal (Hf e Zr) por V nas amostras M1-xVxB2, gera distorções da rede cristalina, com o surgimento de um estado supercondutor volumétrico. As medidas magnéticas, elétricas e térmicas revelam um Tc máximo atingindo 8,7 e 9,3 K para as respectivas amostras de composição Zr0,96V0,04B2 e Hf0,97V0,03B2, com valores elevados de ? 0Hc2(0) (~16 e ~21 T, respectivamente). Nessas amostras, os resultados a cerca do comportamento do ? 0Hc1 (T), do Cp(T) e da VHall (T), e medidas de ETS (electronic tunneling spectroscopy) em um monocristal, revelam a claras assinaturas da supercondutividade multibanda, tal como é reportado para o MgB2. Ainda, resultados mostram a que a existência do estado supercondutor no ZrB2 parece não ser uma exclusividade da substituição por V, já que é observada também na amostra de Zr0,96Y0,04B2, cujo Tc atinge 6,7 K novamente com assinatura de comportamento multibanda. Também são mostrados os resultados da existência dos comportamentos magnéticos competitivos nas amostras do sistema Zr1-xAlxB2, com um surpreendente ordenamento ferromagnético. Nesse mesmo cenário, também é mostrado que substituição de Nb por Ni é hábil em elevar a temperatura crítica do composto NbB2-? de 3,6 K para 6,0 K. Já em outros boretos, como nos sistemas Th1-xMxB12 (M = Zr, Sc, Y, Ti Hf) em condições especiais de síntese e substituição a fase ThB12 (inexistente no equilíbrio) pode ser estabilizada, onde se observa para amostra Th0,97Zr0,03B12 um Tc próximo a 5,5 K e comportamento supercondutor BCS, porém com um baixo valor do parâmetro k o que abre discussão para uma classe nova de supercondutores do tipo 1,5. / The diborides group isostructural to MgB2 represented by AlB2 prototype structure are considered important candidates for superconductivity. However, the existence of the superconducting state is a rare phenomenon in this group of materials, indeed the majority of transition metal diborides are characterized by a Tc lower than 0.7 K. In this group, the normal compounds HfB2, VB2, YB2, and ZrB2 exhibit signature Pauli paramagnetic behavior at low temperatures. In this work it is shown that the metal partial substitution (Hf and Zr) by V in M1-xVxB2 samples generates distortions of the crystal lattice, with the emergence of a bulk superconducting state. The magnetic, electric and thermal measurements reveal a maximum Tc reaching 8.7 and 9.3 K for the respective samples Zr0.96V0.04B2 and Hf0.97V0.03B2 composition with high values of ? 0Hc2(0) (~ 16 and ~ 21 T, respectively). In these samples, the results about the behavior ? 0Hc1 (T), Cp(T), and VHall (T); and ETS (electronic tunneling spectroscopy) measurements in a single crystal; reveal a clear signatures of multiband superconductivity such as reported to the MgB2. Furthermore, the results show that the existence of the superconducting state ZrB2 appears to be not exclusive by V substitution, it is also observed in the sample Zr0.96Y0.04B2 whose Tc reaches 6.7 K again with signature multiband behavior. Also shown are the results of the existence of competitive magnetic behavior in samples of Zr1-xAlxB2 system, with a surprising ferromagnetic ordering. In this same scenario, it is also shown that substitution of Nb by Ni is able to raise the critical temperature of the NbB2-? compound from 3.6 K to 6.0 K. Since other borides as in Th1- xMxB12 (M = Zr, Sc, Y, Ti Hf) systems, in special conditions of synthesis and substitution the ThB12 phase (non-existent in the equilibrium conditions) can be stabilized, which is observed to Th0.97Zr0.03B12 sample with Tc close to 5.5 K and BCS superconducting behavior, but with a low of the k parameter value opening discussion for a new class of 1.5 type superconductors.

In the present work, growth and structural characterization of CrB2/TiB2 superlattices on (0001) Al2O3 substrate is studied. The superlattices are grown using a direct current magnetron sputtering (DCMS) system with a base pressure of <9E-7 Torr. For structural characterization X-ray diffraction (XRD), X-ray reflectivity (XRR), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), and scanning transmission electron microscopy (STEM) are used. Hardness is measured using nanoindentation technique. For growth of CrB2/TiB2 superlattices it is shown that the sputtering gas pressure of PAr= 4 mTorr, and substrate temperature of T= 600 °C are optimized parameters for growing well-structured superlattices with good interface quality. Superlattices with a layer thickness ratio of Γ= 0.43 (Γ= DTiB2/DCrB2+DTiB2) and a total thickness of 1 μm are deposited with different modulation periods Λ=1, 2, 6, 8, and 10 nm to see the layer-thickness affect on the quality of the structures. XRD and TEM results show that by increasing the modulation period, the quality of superlattices with smooth interfaces increases. The superlattices with modulation period Λ=8 nm is shown to be the best structure having coherent lattice and smooth interfaces up to ~20 periods. The STEM analysis shows that after about 20 periods, grains started to grow at slightly different orientations. A superlattice of TiB2/CrB2(having TiB2 as the first deposited layer) with modulation period Λ=8 nm shows an epitaxial growth of TiB2 on Al2O3 (0001) substrate, however, no big difference between the structure of TiB2/CrB2 and CrB2/TiB2 superlattices is seen. EDX maps and line profiles show that there is a diffusion of CrB2 into TiB2 layers which is a serious problem for obtaining sharp interfaces. STEM also shows that for a small modulation period of Λ=1 nm, there is a faint layered structure, whereas EDX, SAED and XRD indicates a homogenous textures Ti-Cr-B film in this sample. Finally, the hardness measurement shows a hardness value of 29-34 GPa for different modulation periods. The lowest hardness value is related to the sample with modulation period of Λ=1 nm with about 29 GPa, and the highest hardness is related to the sample with Λ=8 nm ith around 34 GPa.

The main focus of this work was to investigate substitution effects on the chemical bonding in compounds of AlB 2 -type and related structure types. Delocalization indices within the QTAIM approach and the topological analysis of the ELI functionals were used as tools to describe the bonding situation in digallides and diborides. Digallides of AlB 2 -type were found only within group I and II; for CaGa 2 (meta-stable phase), SrGa 2 , BaGa 2 , YGa 2 and LaGa 2 compounds. Within these compounds, QTAIM analysis showed similar trend as previously found in diborides. That is, along the period in the Periodic Table, metal-triel interactions increase at the expense of in-plane (triel-triel) ab interactions (Tr=triel). However, transition metal diborides adopt the AlB 2 -type up to group VI. To understand this difference, we simulated transition metal (TM) digallides and diborides up to group VI in the AlB 2 -type. Additionally, the puckered variants diborides ReB 2 and OsB 2 were also simulated in the AlB 2 -type. With filling of d shell, there is a delicate balance between increase of TM–Tr and decrease of in-plane (Tr–Tr) ab electron sharing. This balance is maintained as long as interlayer interactions in the c direction (Tr–Tr ) c and (TM–TM ) c are not relatively too high in comparison to in-plane electron sharing. In contrast to TM B 2 of AlB 2 -type, digallides in the same structure type build up strong interlayer interactions for early transition metal elements. Our results showed that within digallides, a relatively strong increase in interlayer electron sharing (Ga–Ga) c and (TM–TM ) c takes place. Such increase occurs already for ScGa 2 and TiGa 2 . On the other hand, diborides show a steady increase in electron sharing of TM –B and (TM–TM ) c , but not of (B–B) c . Therefore, it is reasonable to suggest that diborides will tend to adopt a 3D network composed of boron and transition metal atoms (ReB 2 and RuB 2 types). The additional high (Ga–Ga) c interlayer interactions indicate a tendency for digallides to form 3D networks composed only by gallium atoms, characteristic of CaGa 2 (CaIn 2 -type) and ScGa 2 (KHg 2 -type). The counterbalancing bonding effects of in-plane and out-of-plane interactions that give the chemical flexibility of the AlB 2 -type in diborides is thus disrupted in AlB 2 -type digallides by a further enhanced degree of interlayer interactions (Ga–Ga) c and (TM –TM ) c . This results in a smaller number of digallides than that of diborides in AlB 2 -type. The most conspicuous difference between diborides and digallides of AlB 2 -type is in the representation of the B – B and Ga – Ga bonds revealed by the ELI- D topology. Whereas AlB 2 -type diborides exhibit one ELI-D attractor at the B – B midpoint, AlB 2 -type digallides exhibit two ELI-D attractors symmetrically opposite around the Ga – Ga bond midpoint. We utilized the E 2 H 4 (E=triel, tetrel ) molecular series in the D 2h point group symmetry as model systems for solid state calculations. In particular, we addressed the appearance of ELI- D double maxima for Ga – Ga, by using orbital decomposition within the ELI framework. The ELI-D topology changes along the 13th group T r 2 H 4 series. Whereas B 2 H 4 and Al 2 H 4 exhibit one ELI-D attractor representing the Tr–Tr bond, Ga 2 H 4 and In 2 H 4 give rise to two ELI-D attractors. Partial ELI-D allows the orbital decomposition of the electron density. Partial ELI-q gives access to the decomposition of a two-particle property, which is given by the Fermi-hole curvature. We have found that the d-orbitals enable the formation of the two ELI-D attractors through pairing contributions. This has a net effect of lowering electron localizability at the Ga – Ga bond midpoint. Namely, the different ELI-D topology of Ga – Ga and B – B bonds stems from the contributions of d-orbitals to orbital pairing. We have also investigated the bonding situation in transition metal diborides of ReB 2 -type (MnB 2 , TcB 2 , ReB 2) and RuB 2 -type (OsB 2 , RuB 2). One can consider these two structure types as an extension of the trend found in TM B 2 of AlB 2 -type: an increase in TM –B interactions and an enhanced three-center bonding. The change in the structure type results in a puckered layer of boron atoms with electrons equally shared between B – B and TM –B. However, TM –B bonds exhibit a high three-center character. The ELI-D/QTAIM intersection technique also revealed a high participation of TM in the B – B bonding basin population. Moreover, ELI-D topology in the ReB 2 -type also discloses a seemingly important Re 3 three-center interaction along the flat layer of Re atoms. Such basin is absent in MnB 2 , which coincides with the fact that MnB 2 was only observed in the AlB 2 -type. In this regard, we concluded that the 3D network consists not only of covalent B – B bonds, but also of TM –B bonds.

abstract: Liquid-phase exfoliation (LPE) is a straightforward and scalable method of producing two-dimensional nanomaterials. The LPE process has typical been applied to layered van der Waals (vdW) solids, such as graphite and transition metal dichalcogenides, which have layers held together by weak van der Waals interactions. However, recent research has shown that solids with stronger bonds and non-layered structures can be converted to solution-stabilized nanosheets via LPE, some of which have shown to have interesting optical, magnetic, and photocatalytic properties. In this work, two classes of non-vdW solids – hexagonal metal diborides and boron carbide – are investigated for their morphological features, their chemical and crystallographic compositions, and their solvent preference for exfoliation. Spectroscopic and microscopic techniques are used to verify the composition and crystal structure of metal diboride nanosheets. Their application as mechanical fillers is demonstrated by incorporation into polymer nanocomposite films of polyvinyl alcohol and by successful integration into liquid photocurable 3D printing resins. Application of Hansen solubility theory to two metal diboride compositions enables extrapolation of their affinities for certain solvents and is also used to find solvent blends suitable for the nanosheets. Boron carbide nanosheets are examined for their size and thickness and their exfoliation planes are computationally analyzed and experimentally investigated using high-resolution transmission electron microscopy. The resulting analyses indicate that the exfoliation of boron carbide leads to multiple observed exfoliation planes upon LPE processing. Overall, these studies provide insight into the production and applications of LPE-produced nanosheets derived from non-vdW solids and suggest their potential application as mechanical fillers in polymer nanocomposites. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2020

Pomocou COHP analýzy sme študovali chemickú väzbu v diboridoch prechodných kovov ako aj v zliatine Ni2MnGa. Elektrónová štruktúra študovaných materiálov bola vypočítaná použitím výpočtov z prvých princípov pomocou metódy PAW. V prípade diboridov tranzitných kovov z výsledkov vyplýva, že sila väzby bór-bór je silne závislá od transferu elektrónov na atómy bóru. Zvyšujúci sa počet valenčných elektrónov v kove spôsobuje destabilizáciu alfa štruktúry kvôli vzájomnej interakcii elektrónov prislúchajúcich jednému atómu (on-site interakcie) v blízkosti Fermiho hladiny. Pre zliatinu s tvarovou pamäťou Ni2MnGa bola použitá metóda DFT+ U upravujúca popis lokalizácie elektrónov. V prípade použitia parametra U na Ni dochádza k destabilizácii kubického austenitu a k stabilizácii tetragonálneho nemodulovaného martenzitu. Naopak, zvýšenie lokalizácie elektrónov mangánu martenzit destabilizuje. Analýza väzieb ukázala, že najsilnejšou väzbou je Ni-Ga s kovalentným charakterom. Zvýšená lokalizácia valenčných elektrónov Mn zvyšuje podiel kovalentnosti Mn-Ni väzby a kovový charakter Ni-Ni väzby. Vplyvom zvýšenej lokalizácie Ni elektrónov sa Mn-Ni väzba stáva viac kovovou.

Em Janeiro de 2001, um supercondutor totalmente novo foi apresentado por Nagamatsu, o diboreto de magnésio (MgB2), com uma temperatura crítica, Tc, surpreendentemente alta de 39 K. Atualmente, o MgB2 é considerado o condutor de alto campo do futuro. É claramente aceito que os valores excepcionais de altos campos magnético crítico superior, Hc2, (Hc2 + (0) ? 40 T para Tc ? 35 - 40 K) mostram que o MgB2 é capaz de substituir o Nb3Sn (Hc2 (0) ? 30 T para Tc ? 18 K) como a escolha para aplicações de altos campos magnéticos. Neste trabalho foram preparadas pastilhas supercondutoras de MgB2 utilizando adições de diboretos metálicos de ZrB2, TaB2, VB2 e AlB2 e adições simultâneas de diboretos metálicos e fontes diversas de carbono, como carbeto de silício, grafite e nanotubos de carbono. O objetivo da adição desses novos elementos foi criar mecanismos para melhorar a capacidade de transporte do material, tanto pela dopagem substitucional como pela geração de defeitos na matriz supercondutora, atuando como eficientes centros de aprisionamento das linhas de fluxo magnético. Para isso foram utilizados dois diferentes métodos de preparação de amostras, insitu e ex-situ. O método de preparação in-situ seguiu padrões convencionais, como mistura em moinho de bola e tratamento térmico em fluxo de argônio. Para a preparação das amostras utilizando-se o método ex-situ foram utilizadas técnicas mais sofisticadas, como moagem de alta energia e tratamento térmico em altas pressões (Hot Isostatic Press, HIP). Em geral, as adições dos diboretos metálicos melhoraram a capacidade de transporte do material em baixos campos, as fontes de carbono aumentaram os valores de densidade de corrente crítica em altos campos magnéticos, enquanto que as combinações das duas adições melhoram a capacidade de transporte, para algumas amostras, em toda a faixa de campo magnético medida. / In January 2001, a new superconductor was presented by Nagamatsu, the magnesium diboride (MgB2), with a critical temperature, Tc, extremely high of 39 K. MgB2 is considered the high field conductor of the future. The exceptional high values of upper critical magnetic field, Hc2, (Hc2 + (0) ? 40 T for Tc ? 35 - 40 K) show that the MgB2 is able to replace the Nb3Sn (Hc2 (0) ? 30 T for Tc ? 18 K) as the choice for applications in high magnetic fields. In this work, superconducting pellets of MgB2 were prepared with addition of other metal diborides of ZrB2, TaB2, VB2, and AlB2, and simultaneous additions of metal diborides and different carbon sources, such as silicon carbide, graphite and carbon nanotubes. The objective of these additions of new elements was to create mechanisms to improve the transport capacity of the material, by substitutional doping and by generation of defects in the superconducting matrix, acting as effective pinning centers of magnetic flux lines. Two different methods for sample preparation were used, the in-situ and the ex-situ method. The in-situ preparation method followed conventional standards, such as powder mixing in a ball mill and heat treatment in argon flow. The ex-situ preparation method used more sophisticated techniques, such as high energy ball milling and heat treatment under high pressures (Hot Isostatic Press, HIP). In general, the additions of metal diborides improved the transport capacity of the material at low fields, the carbon sources increased the critical current density at high magnetic fields, whereas the combination of these two additions improved the transport capacity, for some samples, in all range of applied magnetic field.

Em Janeiro de 2001, um supercondutor totalmente novo foi apresentado por Nagamatsu, o diboreto de magnésio (MgB2), com uma temperatura crítica, Tc, surpreendentemente alta de 39 K. Atualmente, o MgB2 é considerado o condutor de alto campo do futuro. É claramente aceito que os valores excepcionais de altos campos magnético crítico superior, Hc2, (Hc2 + (0) ? 40 T para Tc ? 35 - 40 K) mostram que o MgB2 é capaz de substituir o Nb3Sn (Hc2 (0) ? 30 T para Tc ? 18 K) como a escolha para aplicações de altos campos magnéticos. Neste trabalho foram preparadas pastilhas supercondutoras de MgB2 utilizando adições de diboretos metálicos de ZrB2, TaB2, VB2 e AlB2 e adições simultâneas de diboretos metálicos e fontes diversas de carbono, como carbeto de silício, grafite e nanotubos de carbono. O objetivo da adição desses novos elementos foi criar mecanismos para melhorar a capacidade de transporte do material, tanto pela dopagem substitucional como pela geração de defeitos na matriz supercondutora, atuando como eficientes centros de aprisionamento das linhas de fluxo magnético. Para isso foram utilizados dois diferentes métodos de preparação de amostras, insitu e ex-situ. O método de preparação in-situ seguiu padrões convencionais, como mistura em moinho de bola e tratamento térmico em fluxo de argônio. Para a preparação das amostras utilizando-se o método ex-situ foram utilizadas técnicas mais sofisticadas, como moagem de alta energia e tratamento térmico em altas pressões (Hot Isostatic Press, HIP). Em geral, as adições dos diboretos metálicos melhoraram a capacidade de transporte do material em baixos campos, as fontes de carbono aumentaram os valores de densidade de corrente crítica em altos campos magnéticos, enquanto que as combinações das duas adições melhoram a capacidade de transporte, para algumas amostras, em toda a faixa de campo magnético medida. / In January 2001, a new superconductor was presented by Nagamatsu, the magnesium diboride (MgB2), with a critical temperature, Tc, extremely high of 39 K. MgB2 is considered the high field conductor of the future. The exceptional high values of upper critical magnetic field, Hc2, (Hc2 + (0) ? 40 T for Tc ? 35 - 40 K) show that the MgB2 is able to replace the Nb3Sn (Hc2 (0) ? 30 T for Tc ? 18 K) as the choice for applications in high magnetic fields. In this work, superconducting pellets of MgB2 were prepared with addition of other metal diborides of ZrB2, TaB2, VB2, and AlB2, and simultaneous additions of metal diborides and different carbon sources, such as silicon carbide, graphite and carbon nanotubes. The objective of these additions of new elements was to create mechanisms to improve the transport capacity of the material, by substitutional doping and by generation of defects in the superconducting matrix, acting as effective pinning centers of magnetic flux lines. Two different methods for sample preparation were used, the in-situ and the ex-situ method. The in-situ preparation method followed conventional standards, such as powder mixing in a ball mill and heat treatment in argon flow. The ex-situ preparation method used more sophisticated techniques, such as high energy ball milling and heat treatment under high pressures (Hot Isostatic Press, HIP). In general, the additions of metal diborides improved the transport capacity of the material at low fields, the carbon sources increased the critical current density at high magnetic fields, whereas the combination of these two additions improved the transport capacity, for some samples, in all range of applied magnetic field.

The main focus of this work was to investigate substitution effects on the chemical bonding in compounds of AlB 2 -type and related structure types. Delocalization indices within the QTAIM approach and the topological analysis of the ELI functionals were used as tools to describe the bonding situation in digallides and diborides. Digallides of AlB 2 -type were found only within group I and II; for CaGa 2 (meta-stable phase), SrGa 2 , BaGa 2 , YGa 2 and LaGa 2 compounds. Within these compounds, QTAIM analysis showed similar trend as previously found in diborides. That is, along the period in the Periodic Table, metal-triel interactions increase at the expense of in-plane (triel-triel) ab interactions (Tr=triel). However, transition metal diborides adopt the AlB 2 -type up to group VI. To understand this difference, we simulated transition metal (TM) digallides and diborides up to group VI in the AlB 2 -type. Additionally, the puckered variants diborides ReB 2 and OsB 2 were also simulated in the AlB 2 -type. With filling of d shell, there is a delicate balance between increase of TM–Tr and decrease of in-plane (Tr–Tr) ab electron sharing. This balance is maintained as long as interlayer interactions in the c direction (Tr–Tr ) c and (TM–TM ) c are not relatively too high in comparison to in-plane electron sharing. In contrast to TM B 2 of AlB 2 -type, digallides in the same structure type build up strong interlayer interactions for early transition metal elements. Our results showed that within digallides, a relatively strong increase in interlayer electron sharing (Ga–Ga) c and (TM–TM ) c takes place. Such increase occurs already for ScGa 2 and TiGa 2 . On the other hand, diborides show a steady increase in electron sharing of TM –B and (TM–TM ) c , but not of (B–B) c . Therefore, it is reasonable to suggest that diborides will tend to adopt a 3D network composed of boron and transition metal atoms (ReB 2 and RuB 2 types). The additional high (Ga–Ga) c interlayer interactions indicate a tendency for digallides to form 3D networks composed only by gallium atoms, characteristic of CaGa 2 (CaIn 2 -type) and ScGa 2 (KHg 2 -type). The counterbalancing bonding effects of in-plane and out-of-plane interactions that give the chemical flexibility of the AlB 2 -type in diborides is thus disrupted in AlB 2 -type digallides by a further enhanced degree of interlayer interactions (Ga–Ga) c and (TM –TM ) c . This results in a smaller number of digallides than that of diborides in AlB 2 -type. The most conspicuous difference between diborides and digallides of AlB 2 -type is in the representation of the B – B and Ga – Ga bonds revealed by the ELI- D topology. Whereas AlB 2 -type diborides exhibit one ELI-D attractor at the B – B midpoint, AlB 2 -type digallides exhibit two ELI-D attractors symmetrically opposite around the Ga – Ga bond midpoint. We utilized the E 2 H 4 (E=triel, tetrel ) molecular series in the D 2h point group symmetry as model systems for solid state calculations. In particular, we addressed the appearance of ELI- D double maxima for Ga – Ga, by using orbital decomposition within the ELI framework. The ELI-D topology changes along the 13th group T r 2 H 4 series. Whereas B 2 H 4 and Al 2 H 4 exhibit one ELI-D attractor representing the Tr–Tr bond, Ga 2 H 4 and In 2 H 4 give rise to two ELI-D attractors. Partial ELI-D allows the orbital decomposition of the electron density. Partial ELI-q gives access to the decomposition of a two-particle property, which is given by the Fermi-hole curvature. We have found that the d-orbitals enable the formation of the two ELI-D attractors through pairing contributions. This has a net effect of lowering electron localizability at the Ga – Ga bond midpoint. Namely, the different ELI-D topology of Ga – Ga and B – B bonds stems from the contributions of d-orbitals to orbital pairing. We have also investigated the bonding situation in transition metal diborides of ReB 2 -type (MnB 2 , TcB 2 , ReB 2) and RuB 2 -type (OsB 2 , RuB 2). One can consider these two structure types as an extension of the trend found in TM B 2 of AlB 2 -type: an increase in TM –B interactions and an enhanced three-center bonding. The change in the structure type results in a puckered layer of boron atoms with electrons equally shared between B – B and TM –B. However, TM –B bonds exhibit a high three-center character. The ELI-D/QTAIM intersection technique also revealed a high participation of TM in the B – B bonding basin population. Moreover, ELI-D topology in the ReB 2 -type also discloses a seemingly important Re 3 three-center interaction along the flat layer of Re atoms. Such basin is absent in MnB 2 , which coincides with the fact that MnB 2 was only observed in the AlB 2 -type. In this regard, we concluded that the 3D network consists not only of covalent B – B bonds, but also of TM –B bonds.