This study investigates the high-pressure chemistry of yttrium hydrides and carbides synthesized using ammonia borane (NH₃BH₃) and paraffin oil as hydrogen sources in laser-heated diamond anvil cells (DACs) under pressures up to 171 GPa and temperatures up to 3000 K. Using synchrotron single-crystal X-ray diffraction (SCXRD), five previously unknown yttrium hydrides (Y₃H₁₁, Y₂H₉, Y₄H₂₃, Y₁₃H₇₅, and Y₄H₂₅), two previously unknown yttrium allotropes (hP3-Y-II and tI8-Y), and a yttrium carbide (YC₂) were identified. These compounds were characterized through experimental data and density functional theory (DFT) calculations. The study also revealed complex phase diversity, variable hydrogen content in yttrium hydrides, and their metallic nature, which pose challenges in identifying superconducting phases and understanding electronic transitions in high-pressure synthesized materials. The yttrium hydrides identified include known phases such as cF4-YH₃ and tI2-YH₃, as well as newly discovered phases with varying hydrogen content. The hydrogen content in these hydrides increases with pressure, from YH₃ at 87 GPa to YH₆.₂₅ at 171 GPa. The yttrium allotropes identified, hP3-Y-II and tI8-Y, exhibit distinct structural characteristics and are thermodynamically stable under high pressure. The yttrium carbide YC₂ was found to form under high pressure and contains a hexagonal close-packed structure of yttrium atoms with carbon atoms in specific Wyckoff positions. The study highlights the complexity of chemical reactions in high-pressure systems and the importance of using SCXRD for accurate structural analysis. The results demonstrate the broad compositional and structural variety of possible phases in the Y-NH₃BH₃ and Y-paraffin oil systems, emphasizing the need for precise characterization methods to understand the properties of high-pressure materials. The findings contribute to the understanding of high-temperature superconductivity and the electronic properties of yttrium hydrides under extreme conditions.This study investigates the high-pressure chemistry of yttrium hydrides and carbides synthesized using ammonia borane (NH₃BH₃) and paraffin oil as hydrogen sources in laser-heated diamond anvil cells (DACs) under pressures up to 171 GPa and temperatures up to 3000 K. Using synchrotron single-crystal X-ray diffraction (SCXRD), five previously unknown yttrium hydrides (Y₃H₁₁, Y₂H₉, Y₄H₂₃, Y₁₃H₇₅, and Y₄H₂₅), two previously unknown yttrium allotropes (hP3-Y-II and tI8-Y), and a yttrium carbide (YC₂) were identified. These compounds were characterized through experimental data and density functional theory (DFT) calculations. The study also revealed complex phase diversity, variable hydrogen content in yttrium hydrides, and their metallic nature, which pose challenges in identifying superconducting phases and understanding electronic transitions in high-pressure synthesized materials. The yttrium hydrides identified include known phases such as cF4-YH₃ and tI2-YH₃, as well as newly discovered phases with varying hydrogen content. The hydrogen content in these hydrides increases with pressure, from YH₃ at 87 GPa to YH₆.₂₅ at 171 GPa. The yttrium allotropes identified, hP3-Y-II and tI8-Y, exhibit distinct structural characteristics and are thermodynamically stable under high pressure. The yttrium carbide YC₂ was found to form under high pressure and contains a hexagonal close-packed structure of yttrium atoms with carbon atoms in specific Wyckoff positions. The study highlights the complexity of chemical reactions in high-pressure systems and the importance of using SCXRD for accurate structural analysis. The results demonstrate the broad compositional and structural variety of possible phases in the Y-NH₃BH₃ and Y-paraffin oil systems, emphasizing the need for precise characterization methods to understand the properties of high-pressure materials. The findings contribute to the understanding of high-temperature superconductivity and the electronic properties of yttrium hydrides under extreme conditions.