We demonstrate that silicon carbide (SiC) with natural isotope abundance can preserve a coherent spin superposition in silicon vacancies over unexpectedly long time approaching 0.1 seconds. The spin-locked subspace with drastically reduced decoherence rate is attained through the suppression of heteronuclear spin cross-talking by applying a moderate magnetic field in combination with dynamic decoupling from the nuclear spin baths. We identify several phonon-assisted mechanisms of spin-lattice relaxation, ultimately limiting quantum coherence, and find that it can be extremely long at cryogenic temperature, equal or even longer than 8 seconds. Our approach may be extended to other polyatomic compounds and open a path towards improved qubit memory for wafer-scale quantum techmologies.PACS numbers: 76.30. Mi, 42.50.Dv, 76.70.Hb Introduction -Long electron quantum coherence in solid-state systems is the ultimate prerequisite for new technologies based on quantum phenomena [1,2]. Particularly, the sensitivity of quantum sensors scales with the electron spin coherence time T 2 [3,4]. One of the common sources of decoherence is the interaction with fluctuating nuclear spins, and the usual way to prolong spin coherence is to perform isotope purification of the crystal. Indeed, the longest electron T 2 times of about 1 s and 0.6 s have been reported for spin-free silicon 28 Si and diamond 12 C crystals, respectively [5,6]. However, isotope purification is a technologically demanding procedure, which is not always possible. Therefore, one of the key challenges in quantum information science is to achieve long-lived spin coherence in natural materials.To address this goal, we combine two approaches. First, we exploit the suppression of mutual spin flip-flop processes between different types of nuclei in binary compounds, which occur in strong enough magnetic fields according to the theoretical simulations of Ref. [7]. Second, we use a periodic train of radiofrequency (RF) pulses to refocus spin coherence and decouple electron spins from inhomogeneous environment, similar to that applied for color centers [6] and quantum dots (QDs) [8].In recent years, SiC is attracting continuously growing interest as a technologically perspective platform for quantum spintronics [9][10][11][12][13][14][15][16][17] with the ability for single spin engineering and control [18][19][20][21]. The longest T 2 in SiC reported to date is 1 ms at cryogenic temperature [19]. We observe that in a finite magnetic field, a coherent spin superposition can be locked over longer time, which continuously increases up to about 75 ms with the number of decoupling pulses. The absence of saturation indicates that the longest possible spin locking time T